Policy Routing Configuration

introduction introduction traditional route forwarding used to involve looking up the routing table based on the destination address of the packet and then forwarding the packet however, an increasing number of users now wish to forward and select routes for packets based on their own defined policies in addition to traditional route forwarding there are two different types of policy based routing supported by the device acl based policy routing primarily used to control the flow of packets acl allows or denies packets passing through network devices and can filter based on conditions such as source ip address, destination ip address, port numbers, etc acl can be combined with policy routing to determine the direction of traffic by matching specific conditions of packets, thus implementing policy routing pbr based policy routing mainly used to select different paths or next hops based on specific policies, rather than solely based on the traditional routing table pbr allows defining the direction of traffic based on conditions such as source ip, destination ip, protocol, port, etc it is a more flexible policy routing mechanism when dealing with smaller network scales and requiring simple traffic filtering and routing control, acl based policy routing can be chosen when there is a need to implement more flexible routing policies such as multipath selection, failover, etc , pbr based policy routing can be chosen explanation of principle explanation of principle policy routing is achieved by configuring redirection in the flow behavior, and it only takes effect on packets incoming on the interface it is a mechanism for forwarding packets based on user defined policies, with a priority higher than directly connected routes, static routes, and routes generated through dynamic routing protocols after configuring policy routing on the device, if the received packet (including layer 2 packets) matches the rules of policy routing, it will be forwarded according to the rules; if the match fails, it will be forwarded according to the normal forwarding process based on the destination address configuration configuration configuration tasks description create and enter the policy routing view mandatory create matching conditions for policy routing mandatory specify the next hop for policy routing optional create a next hop address group and enter the view optional bind the policy routing to a specified interface optional creating policy route creating policy route operation command description enter the system configuration view configure terminal create and enter the policy routing view pbr map name seq number name specifies the name of the policy number policy id, with a range of 1 700 the lower the number, the higher the priority creating matching conditions for policy route creating matching conditions for policy route operation command description enter policy route view pbr map name seq number create matching conditions for policy route match {dst ip ip address |dst port port |ip protocol protocol |src ip ip address |src port port } dst ip ip address match the destination ip address of the packet dst port port match the destination port number of the packet ip protocol protocol match the protocol type of the packet src ip ip address match the source ip address of the packet src port port match the source port number of the packet specifying the next hop for policy route specifying the next hop for policy route the "nexthop" command supports configuring up to 4 next hops when multiple next hops are configured, packets are redirected and forwarded in a primary backup manner the primary and backup links are determined based on the configuration order, where the next hop ip address configured first has a higher priority as the primary link in the event of a failure in the primary link, the backup link is automatically selected in order of configuration as the new primary link operation command description enter policy route view pbr map name seq number specify the next hop for policy route set {nexthop ip address |nexthop group name } nexthop ip address specifies the ip address of the next hop nexthop group specifies the name of the next hop address group creating next hop address group and entering the view creating next hop address group and entering the view when the next hop for policy routing is an address group, packets will be load balanced among the different next hops within the address group operation command description enter the system configuration view configure terminal create next hop address group nexthop group name configure member addresses in the next hop address group nexthop ip address binding the policy route to a specified interface binding the policy route to a specified interface operation command description enter the interface view interface ethernet interface id bind the policy route to a specified interface pbr policy name display and maintenance display and maintenance operation command view the binding relationship between policy routing and interfaces show pbr interface \[ interface name ] view configured policy routes show pbr map \[ map name ] view next hop address groups for policy routing show pbr nexthop groups configuration example configuration example network requirements network requirements control the packets received from interface vlan11 of switch a using policy based routing specify the next hop for all tcp packets as 1 1 2 2 forward other packets using the traditional route table lookup method switch a is directly connected to switch b and switch c there is no reachable route between switch b and switch c host a can successfully telnet to switch b but cannot telnet to switch c additionally, host a can ping both switch b and switch c procedure procedure ip addresses and vlan configuration omitted configuration on switch a \# create pbr rule sonic(config)# pbr map aaa seq 5 sonic(config pbr map)# match ip protocol tcp sonic(config pbr map)# set nexthop 1 1 2 2 sonic(config pbr map)# exit \# apply the policy route map to interface sonic(config)# interface vlan 11 sonic(config vlanif 11)# ip address 10 110 0 10/24 sonic(config vlanif 11)# pbr policy aaa sonic(config vlanif 11)# exit \# configuration on switch b and switch c for static routes to host a sonic(config)# ip route 10 110 0 0/24 1 1 2 1 sonic(config)# ip route 10 110 0 0/24 1 1 3 1 verify configuration verify configuration verify the configuration sonic# show pbr map detail pbr map aaa valid yes seq 5 rule 304 installed 2(1) reason valid ip protocol match tcp nexthop 1 1 2 2 installed 1(1) tableid 10000 perform telnet and ping from host a, and verify if the results match the expectations telnet from host a to switch b (telnet 1 1 2 2) success telnet from host a to switch c (telnet 1 1 3 2) failure ping from host a to switch c (ping 1 1 3 2) success