IS-IS Configuration Guide

introduction introduction is is (intermediate system to intermediate system) is a dynamic routing protocol designed by the international organization for standardization (iso) for its connectionless network protocol clnp (connect less network protocol) it is an internal gateway protocol (igp) based on link state, used for routing exchange within autonomous systems is is operates at the data link layer and uses the shortest path first (spf) algorithm for routing calculations it has the advantages of fast convergence, strong scalability, strong resistance to attacks, and can achieve interoperability in large scale networks with the widespread application of the tcp/ip protocol, the ietf organization expanded and modified is is in rfc1195, enabling it to be applied simultaneously in both tcp/ip and osi (open system interconnection) environments, known as integrated is is or dual is is basic concepts basic concepts is is area is is area is is adopts a hierarchical structure of backbone and non backbone regions within the autonomous system level 1 routers are deployed in non backbone areas, while level 2 routers and level 1 2 routers are deployed in backbone areas each non backbone area is connected to the backbone area through level 1 2 routers area differences between is is and ospf all interfaces of a single router in is is belong to the same area different interfaces of a single router in ospf can belong to different regions in is is, there is no distinction between backbone and non backbone areas for a single region backbone area in ospf refers to the area with area 0 both level 1 and level 2 routing in is is use spf algorithm to generate shortest path tree (spt) for each level in ospf, the spf algorithm is only used within the same area, and routing between areas needs to be forwarded through the backbone area is is router type is is router type there are three different routers in is is network level 1，level 2，level 1 2 level 1 router responsible for routing within the region, it only forms neighbor relationships with level 1 and level 1 2 routers belonging to the same region a level 1 router is only responsible for maintaining the lsdb (link state database) within its own area for routes whose destination is not within its own area, the level 1 router will identify the destination as the nearest level 1 2 router level 2 router responsible for routing between regions, can form neighbor relationships with level 2 or level 1 2 routers in other regions, and maintain a level 2 lsdb that contains routing information between regions all level 2 level routers form the backbone network of the routing domain, responsible for communication between different areas level 2 level routers in the routing domain must be physically continuous to ensure the continuity of the backbone network only level 2 level routers can directly exchange data packets or routing information with routers outside the region level 1 2 router a router that belongs to both level 1 and level 2 is called a level 1 2 router it can form a level 1 neighbor relationship with level 1 and level 1 2 routers in the same area, or form a level 2 neighbor relationship with level 2 and level 1 2 routers in other areas level 1 routers must pass through level 1 2 routers to connect to other areas level 1 2 routers maintain two lsdbs, with level 1 lsdb used for intra area routing and level 2 lsdb used for inter area routing is is network type is is network type is is supports two types of networks, which can be divided into broadcast networks and point to point networks based on different physical links broadcast network running on broadcast links such as ethernet, token ring, etc point to point network runs on point to point links such as ppp, hdlc, etc in broadcast networks, is is needs to select one router from all routers as the designated intermediate system (dis) dis is used to create and update pseudo nodes, and is responsible for generating link state protocol data units (lsps) for pseudo nodes, which describe the network devices on this network pseudo nodes are virtual nodes used to simulate broadcast networks, not real routers in is is, pseudo nodes are identified by the system id of dis and a byte of circuit id (non zero value) level 1 and level 2 dis are elected separately, and users can set different priorities for dis elections at different levels the one with the highest dis priority value is selected as dis if there are multiple routers with the highest priority value, the router with the highest mac address will be selected different levels of dis can be the same router or different routers differences between is is dis and ospf dr in the is is broadcast network, routers with priority 0 participate in the election of dis routers with priority 0 in ospf do not participate in dr elections in the is is broadcast network, when a newly added router meets the conditions to become a dis, it will be selected as the new dis, and the original pseudo nodes will be deleted this change will cause a new set of lsps to flood in ospf, a newly added router will not immediately become a dr in the network even if it has the highest dr priority value in the is is broadcast network, adjacency relationships are formed between routers of the same level on the same network segment, including all non dis routers in ospf, routers only establish adjacency relationships with dr and bdr is is net identifier is is net identifier network service access point (nsap) is an address used in the osi protocol to locate resources, and its structure is shown in the following figure idp (initial domain part) consists of two parts afi (authority and format identifier) and idi (initial domain identifier) afi stands for address allocation authority and address format, while idi is used to identify domains the dsp (domain specific part) consists of three parts high order dsp, system id, and sel high order dsp is used to divide regions, system id is used to distinguish hosts, and sel (nsap selector) is used to indicate service types area address is composed of idp and high order dsp in dsp, equivalent to area id in ospf all routing devices within the same level 1 area must have the same area address, while routing devices within level 2 area can have different area addresses the system id is used to uniquely identify a host or routing device within a region, and in device implementation, its length is fixed at 48 bits (6 bytes) in practical use, the following method can be used to correspond to the device router id and system id expand each part of ip address 10 1 0 1 to 3 bits, i e 010 001 000 001, and redivide the extended port address into 3 parts to obtain 0100 0100 0001 as the system id sel(nsap selector）,similar to the ip protocol field in the ip protocol, sel is 00 in the ip network net (network entity title) is a special type of nsap (sel=00) that uniquely identifies routers in is is networks is is message type is is message type is is defines 9 types of pdus, which can be divided 3 categories based on their functions hello, lsp, snp table 1 is is message type table 1 is is message type is is message pdu type pdu type value description hello l1 hello 15 used to establish level 1 neighbors on broadcast type links l2 hello 16 used to establish level 2 neighbors on broadcast type links p2p hello 17 used to establish level 1 and level 2 neighbors on point to point links lsp l1 lsp 18 used to describe the link status table of non backbone areas l2 lsp 20 used to describe the status table of backbone area links snp l1 csnp 24 l1 level complete sequence number pdu, similar to ospf dd message l2 csnp 25 l2 level complete sequence number pdu, similar to ospf dd message l1 psnp 26 partial sequence number pdu at l1 level, similar to ospf's lsr and lsack l2 psnp 27 partial sequence number pdu at l2 level, similar to ospf's lsr and lsack on the broadcast network link, csnp is periodically sent by dis devices when neighbors discover that lsdb is not synchronized, they send psnp messages to request missing lsp messages on the point to point chain, csnp only sends when establishing a neighbor relationship for the first time, and the neighbor sends psnp messages as a response when neighbors discover that lsdb is not synchronized, they also send psnp messages to request missing lsp messages is is neighbor status is is neighbor status in the is is network, two routers need to form a neighbor relationship to exchange routing information is is defines three neighbor states down, initial, and up table 2 is is neighbor status table 2 is is neighbor status neighbor status description down at the initial stage of neighbor conversation, it indicates that no active neighbors have been detected initial received a hello message from a neighbor that does not contain its own information, and the status is initial at this time up received a hello message from a neighbor containing its own information, with the status being up the neighbor establishment on the broadcast link adopts a three time handshake mechanism the following figure shows the process of is is neighbor state changes on the broadcast link there are two handshake mechanisms and three handshake mechanisms for establishing neighbors on a point to point chain two handshakes if a hello message is received from the other end, the neighbor status will be up triple handshake both neighbors send p2p hello messages three times to establish a neighbor relationship, similar to the process of establishing neighbors on a broadcast link is is authentication method is is authentication method there are three authentication methods for is is interface authentication, area authentication, and routing domain authentication these three authentication methods can all choose to use plaintext authentication and md5 authentication clear text authentication directly adds the configured password to the message, which will be determined by the network detector, so it is not secure md5 authentication applies the md5 algorithm to the configured password before adding it to the message, which enhances the security of the password table 3 is is authentication method table 3 is is authentication method authentication method description interface authentication encapsulate authentication information in is is hello messages, only authenticated messages will be received by neighboring routing devices, and neighbor relationships can be established area authentication encapsulate the authentication password in is is csnp, psnp, and lsp messages in level 1 area, and only authenticated messages will be received route domain authentication encapsulate the authentication password in is is csnp, psnp, and lsp messages in level 2 area, and only authenticated messages will be received is is route cost is is route cost in the early days of iso10589, the maximum cost value that could be configured under an interface that enabled the is is protocol was 63, and the is is cost type was considered narrow however, in large scale network design, a smaller measurement range cannot meet practical needs so in rfc3784, it is specified that the interface cost value for enabling the is is protocol can be extended to 16777215, and the is is routing cost value can reach 4261412864 at this point, the cost of is is is wide there are differences in tlvs that can be configured for different types of expenses tlvs used for narrow types are 128 tlv (ip internal reachability tlv) 128 tlv (ip internal reachability tlv) used to carry is is routing information within the routing domain 130 tlv (ip external reachability tlv) 130 tlv (ip external reachability tlv) used to carry is is routing information outside the routing domain 2 tlv 2 tlv used to carry neighbor information tlvs used under wide type 35 tlv (extended ip reachability tlv) 35 tlv (extended ip reachability tlv) used to replace the original ip reachability tlv, it carries is is routing information, expands the range of routing overhead values, and can carry sub tlvs 22 tlv (is extended neighbors tlv) 22 tlv (is extended neighbors tlv) used to carry neighbor information is is under wide type and is is under narrow type cannot achieve interoperability if interoperability is required, it must be set to a consistent overhead type so that all routers on the network can receive all packets sent by other routers when configuring the cost type as compatible, a message will be sent separately for narrow and wide types isis router overload isis router overload is is uses the is is overload flag to identify overload status the is is overload flag refers to the ol field in the is is lsp message after setting the overload flag on the device, other devices will not use this device for forwarding during spf calculation, only calculating the direct route on this device when the system is unable to save a new lsp for various reasons, resulting in the inability to maintain normal lsdb synchronization, the routing information calculated by the system will be incorrect in this case, the system can automatically enter an overload state, where the route reached through the device is not calculated, but the direct connection route of the device will not be ignored n addition to automatic overload caused by device abnormalities, the system can also be manually configured to enter an overload state when certain is is devices in the network need to be upgraded or maintained, they need to be temporarily isolated from the network at this point, an overload flag can be set for the device to prevent other devices from forwarding traffic through the node is is configuration is is configuration prerequisite configure the interface ip to make the network layer of adjacent nodes reachable table 4 overview of is is configuration tasks table 4 overview of is is configuration tasks configuration tasks description refer to is is basic functions enable is is required docid\ l3ias1vjnxhkxdqhfobhd interface enable is is function required docid\ l3ias1vjnxhkxdqhfobhd configure is is level optional docid\ l3ias1vjnxhkxdqhfobhd configure interface is is level optional docid\ l3ias1vjnxhkxdqhfobhd configure is is metric type optional docid\ l3ias1vjnxhkxdqhfobhd configure is is interface metric optional docid\ l3ias1vjnxhkxdqhfobhd configure is is network type optional docid\ l3ias1vjnxhkxdqhfobhd configure is is lsp parameters optional docid\ l3ias1vjnxhkxdqhfobhd configure is is neighbor detection parameters optional docid\ l3ias1vjnxhkxdqhfobhd config is is dis election priority optional docid\ l3ias1vjnxhkxdqhfobhd configure is is interface authentication optional docid\ l3ias1vjnxhkxdqhfobhd configure is is area authentication optional docid\ l3ias1vjnxhkxdqhfobhd configure is is route area authentication optional docid\ l3ias1vjnxhkxdqhfobhd configure is is default route optional docid\ l3ias1vjnxhkxdqhfobhd introduce other protocols route optional docid\ l3ias1vjnxhkxdqhfobhd configure is is and bfd linkage optional docid\ l3ias1vjnxhkxdqhfobhd is is default setting is is default setting table 5 isis default setting table 5 isis default setting parameter default value isis disable dis priority 64 level level 1 2 is is network type broadcast is is cost type wide is is interface cost 10 is is time interval hello message time interval 3scnsp message time interval 10shello message timeout 30slas message update interval 900slsp maximum survival time 1200s enable is is enable is is table 6 enable is is table 6 enable is is purpose commands description enter global configuration view configure terminal configure is is packet trap to cpu isis enable default disable enter is is configuration view router isis area tag \[ vrf vrf name ] configure net net xx xxxx xxxx xxxx xxxx xx 1) the system id part in net uniquely identifies a router in the network 2) the last two fixed digits of net under ip network are 00 enable interface is is enable interface is is table 7 enable interface is is table 7 enable interface is is purpose commands description enter global configuration view configure terminal enter interface configuration view interface { ethernet interface name \[ subinterface number ] | link aggregation lag id \[ subinterface number ]| vlan vlan id } enable interface is is ip router isis area tag configure is is level configure is is level table 8 configure is is level table 8 configure is is level purpose commands description enter global configuration view configure terminal enter is is configuration view router isis area tag \[ vrf vrf name ] configure is is level is type { level 1 | level 1 2 | level 2 only } the default level is level 2 note during network operation, changing the level of is is devices may cause disconnection of is is neighbors it is recommended that users complete device level configuration when configuring is is configure interface is is level configure interface is is level table 9 configure interface is is level table 9 configure interface is is level purpose commands description enter global configuration view configure terminal enter interface configuration view interface { ethernet interface name \[ subinterface number ] | link aggregation lag id \[ subinterface number ]| vlan vlan id } configure interface is is level isis circuit type { level 1 | level 1 2 | level 2 only } note： changing the level of the interface only makes sense when the level of the is is device is level 1 2, otherwise the level of neighbor relationships that the interface can establish will be determined by the level of the is is device configure is is metric type configure is is metric type table 10 configure is is metric type table 10 configure is is metric type purpose commands description enter global configuration view configure terminal enter is is configuration view router isis area tag \[ vrf vrf name ] configure is is metric style metric style { narrow | transition | wide } configure interface is is metric configure interface is is metric table 11 configure interface is is metric table 11 configure interface is is metric purpose commands description enter global configuration view configure terminal enter interface configuration view interface { ethernet interface name \[ subinterface number ] | link aggregation lag id \[ subinterface number ]| vlan vlan id } configure interface is is metric isis metric \[ level 1 | level 2 ] metric value the value of metric value is related to the is is overhead type when the cost type is narrow, the cost value range is \[0,63] when the cost type is wide, the cost value range is \[0, 16777215] configure is is network type configure is is network type table 12 configure is is network type table 12 configure is is network type purpose commands description enter global configuration view configure terminal enter interface configuration view interface { ethernet interface name \[ subinterface number ] | link aggregation lag id \[ subinterface number ]| vlan vlan id } configure is is network type isis network point to point the default network type is broadcast configure is is lsp parameters configure is is lsp parameters table 13 configure is is lsp parameters table 13 configure is is lsp parameters purpose commands description enter global configuration view configure terminal enter is is configuration view router isis area tag \[ vrf vrf name ] configure the minimum interval for is is to generate lsp messages lsp gen interval \[ level 1 | level 2 ] seconds the value range of seconds is \[1,120] configure the maximum length of lsp messages generated by is is lsp mtu mtu the value range of mtu is \[128,4352] configure lsp maximum survival time max lsp lifetime \[ level 1 | level 2 ] seconds the value range of seconds is \[350,65235] configure lsp refresh time lsp refresh interval \[ level 1 | level 2 ] seconds the value range of seconds is \[1,65235] configure the minimum calculation interval for spf spf interval \[ level 1 | level 2 ] seconds the value range of seconds is \[128,4352] configure is is neighbor detection parameters configure is is neighbor detection parameters table 14 configure is is neighbor detection parameters table 14 configure is is neighbor detection parameters purpose commands description enter global configuration view configure terminal enter interface configuration view interface { ethernet interface name \[ subinterface number ] | link aggregation lag id \[ subinterface number ]| vlan vlan id } configure is is hello message interval isis hello interval \[ level 1 | level 2 ] seconds the value range of seconds is \[1,600] configure is is hello detection multiplier isis hello multiplier \[ level 1 | level 2 ] times the value range of time is \[2,100] configure is is dis election priority configure is is dis election priority table 15 configure is is dis election priority table 15 configure is is dis election priority purpose commands description enter global configuration view configure terminal enter interface configuration view interface { ethernet interface name \[ subinterface number ] | link aggregation lag id \[ subinterface number ]| vlan vlan id } configure is is dis election priority isis priority priority the value range of priority is \[0,127] configure is is interface authentication configure is is interface authentication table 16 configure is is interface authentication table 16 configure is is interface authentication purpose commands description enter global configuration view configure terminal enter interface configuration view interface { ethernet interface name \[ subinterface number ] | link aggregation lag id \[ subinterface number ]| vlan vlan id } configure is is interface authentication isis password { clear | md5 } password configure is is area authentication configure is is area authentication table 17 configure is is area authentication table 17 configure is is area authentication purpose commands description enter global configuration view configure terminal enter is is configuration view router isis area tag \[ vrf vrf name ] configure is is area authentication area password { clear | md5 } password \[ authenticate snp { send only | validate }] note when authentication is required for level 1 areas, is is area authentication needs to be configured after configuring the area password command, is is waits for all unauthenticated level 1 lsp messages in the local lsdb to automatically age before discarding them configure is is route area authentication configure is is route area authentication table 18 configure is is route area authentication table 18 configure is is route area authentication purpose commands description enter global configuration view configure terminal enter is is configuration view router isis area tag \[ vrf vrf name ] configure is is route area authentication domain password { clear | md5 } password \[ authenticate snp { send only | validate }] note when authentication is required for level 2 areas, is is routing domain authentication needs to be configured after configuring the domain password command, is is waits for automatic aging of all unauthenticated level 2 lsp messages and newly received unauthenticated level 2 lsp and snp messages in the local lsdb before discarding them configure is is default route configure is is default route table 19 configure is is default route table 19 configure is is default route purpose commands description enter global configuration view configure terminal enter is is configuration view router isis area tag \[ vrf vrf name ] configure is is default route default information originate { ipv4|ipv6 } { level 1|level 2 } always \[ metric metric value ] \[ route map route map name ] introduce other protocols route introduce other protocols route table 20 introduce other protocols route table 20 introduce other protocols route purpose commands description enter global configuration view configure terminal enter is is configuration view router isis area tag \[ vrf vrf name ] introduce other protocols route redistribute { ipv4|ipv6 } { ospf | kernel|connected|static|rip|bgp } { level 1 | level 2 } \[ metric metric value ] \[ route map route map name ] configure is is and bfd linkage configure is is and bfd linkage table 21 configure is is and bfd linkage table 21 configure is is and bfd linkage purpose commands description enter global configuration view configure terminal enter interface configuration view interface { ethernet interface name \[ subinterface number ] | link aggregation lag id \[ subinterface number ]| vlan vlan id } configure is is and bfd linkage isis bfd configure the profile for binding bfd isis bfd profile profile name bind user defined bfd profile to modify bfd session parameters the default bfd parameter is 3 × 300ms display and maintenance display and maintenance able 22 is is display and maintenance able 22 is is display and maintenance purpose command description show is is neighbor information show isis \[ vrf vrf name ] neighbor \[options] the options for option are as follows\ detail displays detailed neighbor information systemid displays information about the neighbors of the specified system id show interface is is information show isis \[ vrf vrf name ] interface \[options] the options for option are as follows\ detail displays detailed interface information show is is route information show isis route \[options] the options for option are as follows\ the level 1 displays the routing information of level 1 neighbors the level 2 displays routing information for level 2 neighbors show is is link status information show isis database \[options] the options for option are as follows\ detail displays detailed information about the link status typical configuration guide typical configuration guide networking requirements hosts from different network segments are connected through three switches, all of which run the is is protocol request to configure is is neighbors so that vm1 attached to switch a can communicate with vm2 attached to switch c topology configuration steps check that the link status of the ports used by the switch is normal, and all ports remain stable in up state configure the interface ip and loopback0 ip of the switch configure the is is level and net of the switch configure is is interface authentication mode and authentication key introducing direct routing in the is is protocol of switch a and c switch a interface loopback 0 ip address 10 245 0 129/32 exit ! interface ethernet 0/80 ip address 10 245 253 1/30 exit ! interface ethernet 0/88 ip address 172 16 10 1/24 exit ! isis enable ! router isis 1 is type level 1 net 10 0000 0102 4500 0129 00 redistribute ipv4 connected level 1 exit ! interface ethernet 0/80 ip router isis 1 isis password md5 12345678 switch b ! interface loopback 0 ip address 10 245 0 169/32 exit ! interface ethernet 0/64 ip address 10 245 253 2/30 exit ! interface ethernet 0/76 ip address 10 245 253 122/30 exit ! isis enable ! router isis 1 net 10 0000 0102 4500 0169 00 exit ! interface ethernet 0/64 ip router isis 1 isis password md5 12345678 exit ! interface ethernet 0/76 ip router isis 1 isis password md5 12345678 exit switch c interface loopback 0 ip address 10 245 0 174/32 exit ! interface ethernet 0/64 ip address 10 245 253 121/30 exit ! interface ethernet 0/88 ip address 172 16 20 1/24 exit ! isis enable ! router isis 1 is type level 1 net 10 0000 0102 4500 0174 00 redistribute ipv4 connected level 1 exit ! interface ethernet 0/64 ip router isis 1 isis password md5 12345678 exit verify the configuration \#check if the is is neighbor relationship has been successfully established switch a switcha# show isis neighbor detail area 1 switchb interface ethernet 0/80, level 1, state up, expires in 28s adjacency flaps 1, last 1h23m34s ago circuit type l1l2, speaks ipv4 snpa 60eb 5a01 30db, lan id 0102 4500 0169 14 lan priority 64, is dis, dis flaps 1, last 1h23m34s ago area address(es) 10 0000 ipv4 address(es) 10 245 253 2 switch b switchb # show isis neighbor detail area 1 switchc interface ethernet 0/76, level 1, state up, expires in 28s adjacency flaps 1, last 6m54s ago circuit type l1, speaks ipv4 snpa 0001 0203 0405, lan id 0102 4500 0169 0d lan priority 64, is not dis, dis flaps 1, last 6m54s ago area address(es) 10 0000 ipv4 address(es) 10 245 253 121 switcha interface ethernet 0/64, level 1, state up, expires in 30s adjacency flaps 1, last 1h24m27s ago circuit type l1, speaks ipv4 snpa 60eb 5a01 1523, lan id 0102 4500 0169 14 lan priority 64, is not dis, dis flaps 1, last 1h24m27s ago area address(es) 10 0000 ipv4 address(es) 10 245 253 1 switch c switchc# show isis neighbor detail area 1 switchb interface ethernet 0/64, level 1, state up, expires in 29s adjacency flaps 1, last 4m7s ago circuit type l1l2, speaks ipv4 snpa 60eb 5a01 30db, lan id ai 169 0d lan priority 64, is dis, dis flaps 1, last 4m7s ago area address(es) 10 0000 ipv4 address(es) 10 245 253 122 \#check for successful is is routing exchange switch a switcha# show ip route isis codes k kernel route, c connected, s static, r rip, o ospf, i is is, b bgp, e eigrp, n nhrp, t table, v vnc, v vnc direct, a babel, f pbr, f openfabric, \> selected route, \\ fib route, q queued, r rejected, b backup t trapped, o offload failure i> 1 1 1 141/32 \[115/20] via 10 245 253 2, ethernet 0/80, weight 1, 00 05 24 i> 10 245 0 174/32 \[115/20] via 10 245 253 2, ethernet 0/80, weight 1, 00 05 24 i 10 245 253 0/30 \[115/20] via 10 245 253 2, ethernet 0/80 inactive, weight 1, 00 05 47 i> 10 245 253 120/30 \[115/20] via 10 245 253 2, ethernet 0/80, weight 1, 00 05 47 i> 10 245 253 124/30 \[115/20] via 10 245 253 2, ethernet 0/80, weight 1, 00 05 24 i> 10 245 253 128/30 \[115/20] via 10 245 253 2, ethernet 0/80, weight 1, 00 05 24 i> 10 245 253 132/30 \[115/20] via 10 245 253 2, ethernet 0/80, weight 1, 00 05 24 i> 10 245 253 136/30 \[115/20] via 10 245 253 2, ethernet 0/80, weight 1, 00 05 24 i> 10 250 0 0/24 \[115/20] via 10 245 253 2, ethernet 0/80, weight 1, 00 05 24 i> 172 0 0 4/30 \[115/20] via 10 245 253 2, ethernet 0/80, weight 1, 00 05 24 i> 172 16 20 0/24 \[115/20] via 10 245 253 2, ethernet 0/80, weight 1, 00 05 24 switch b switchc# show ip route isis codes k kernel route, c connected, s static, r rip, o ospf, i is is, b bgp, e eigrp, n nhrp, t table, v vnc, v vnc direct, a babel, f pbr, f openfabric, \> selected route, \\ fib route, q queued, r rejected, b backup t trapped, o offload failure i> 1 1 1 129/32 \[115/20] via 10 245 253 122, ethernet 0/64, weight 1, 00 05 58 i> 10 245 0 129/32 \[115/20] via 10 245 253 122, ethernet 0/64, weight 1, 00 05 58 i> 10 245 253 0/30 \[115/20] via 10 245 253 122, ethernet 0/64, weight 1, 00 05 58 i> 10 245 253 4/30 \[115/20] via 10 245 253 122, ethernet 0/64, weight 1, 00 05 58 i> 10 245 253 8/30 \[115/20] via 10 245 253 122, ethernet 0/64, weight 1, 00 05 58 i> 10 245 253 12/30 \[115/20] via 10 245 253 122, ethernet 0/64, weight 1, 00 05 58 i> 10 245 253 16/30 \[115/20] via 10 245 253 122, ethernet 0/64, weight 1, 00 05 58 i 10 245 253 120/30 \[115/20] via 10 245 253 122, ethernet 0/64 inactive, weight 1, 00 05 58 i> 172 0 0 0/30 \[115/20] via 10 245 253 122, ethernet 0/64, weight 1, 00 05 58 i> 172 16 10 0/24 \[115/20] via 10 245 253 122, ethernet 0/64, weight 1, 00 05 58 172 16 10 0/24 is the direct connection network segment of switch a, and 172 16 20 0/24 is the direct connection network segment of switch c this indicates that both switch a and switch c have obtained each other's direct connection route through is is \#use the ping command to verify connectivity vm1# ping 172 16 20 2 src 172 16 10 2 ping 172 16 20 2 (172 16 20 2) from 172 16 10 2 56(84) bytes of data 64 bytes from 172 16 20 2 icmp seq=1 ttl=64 time=0 580 ms 64 bytes from 172 16 20 2 icmp seq=2 ttl=64 time=32 3 ms 64 bytes from 172 16 20 2 icmp seq=3 ttl=64 time=0 374 ms 64 bytes from 172 16 20 2 icmp seq=4 ttl=64 time=2 68 ms 64 bytes from 172 16 20 2 icmp seq=5 ttl=64 time=15 0 ms \ 172 16 20 2 ping statistics 5 packets transmitted, 5 received, 0% packet loss, time 4032ms rtt min/avg/max/mdev = 0 374/10 174/32 259/12 289 ms vm1 and vm2 can ping each other