Understanding Nexus -- Part 18 -- RIP

RIP is Routing Information Protocol which uses User Datagram Protocol (UDP) packets to exchange routing information. It’s usually used in very small networks.

Note: Cisco NX-OS does not support IPv6 for RIP.

Here we will discuss on RIPv2 since Cisco NX-OS does not support RIPv1. If it receives a RIPv1 packet, it logs a message and drops that packet. Also NX-OS does not establish adjacencies with RIPv1 routers.

RIP uses the two message types:

Request Message - Sent to the multicast address 224.0.0.9 to request route updates from other RIP-enabled routers.

Response Message - Sent every 30 seconds by default. Response messages are also sent after router receives a Request message. It contains the entire RIP routing table. RIP process sends multiple response packets, if the RIP routing table is big and cannot fit in single packet.

RIP uses a hop count as a routing metric. The hop count is the number of routers that a packet can traverse before reaching its destination. A directly connected network has a metric of 1; an unreachable network has a metric of 16.

Authentication

RIPv2 supports authentication. NX-OS supports a simple password or an MD5 authentication.

RIP authentication can be configured on per interface basis by using key-chain. The encrypted password is used with all RIP messages (Request or Response).

Split Horizon

Split horizon is a method that controls the sending of RIP updates and query packets. When you enable split horizon on an interface, Cisco NX-OS does not send update packets for destinations that were learned from this interface.

By default, split horizon is enabled on all interfaces.

Summarization

You can configure multiple summary aggregate addresses for a specified interface. If more specific routes are present in the routing table, RIP advertises the summary address from the interface with a metric equal to the smallest metric of the specific routes.

Note: Cisco NX-OS does not support automatic route summarization.

Load Balancing

NX-OS supports the Equal Cost Multiple Paths (ECMP) feature with up to 16 equal-cost paths in the RIP route table and the unicast RIB.

Configuring RIP

switch# config t
switch(config)# feature rip
switch(config)# router RIP Enterprise
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)# distance 30
switch(config-router-af)# max-paths 10

Adding an Interface

Here we have to add an interface to the routing process.

switch# config t
switch(config)# interface ethernet 1/2
switch(config-if)# ip router rip Enterprise

Configuring RIP Authentication

To configure authentication, first create a Key.

switch# conf t
switch(config)# key chain rip-keys
switch(config-keychain)# key 13
switch(config-keychain-key)# key-string 0 Secure-Key

Apply it on the interface

switch# config t
switch(config)# interface ethernet 1/2
switch(config-if)# ip rip authentication mode md5
switch(config-if)# ip rip authentication keychain rip-keys

Passive Interface

You can configure a RIP interface to receive routes but not send route updates by setting the interface to passive mode.

switch(config-if)# ip rip passive-interface

Configuring Split Horizon with Poison Reverse

Split Horizon is enabled by default. But still you can configure poison-reverse on an interface to advertise routes with unreachable metric.

switch(config-if)# ip rip poison-reverse

Configuring Summarization

NX-OS advertises the summary address metric that is the smallest metric of all the specific routes.

switch(config-if)# ip router rip summary-address 192.0.2.0/24

Tuning RIP

RIP uses several timers that determine the frequency of routing updates, the length of time before a route becomes invalid, and other parameters. You can adjust these timers as per your network requirements.

switch(config-router-af)# timers basic 30 180 180 120

update - determine the frequency of routing updates, The range is from 5 to any positive integer. The default is 30.

Timeout - time that Cisco NX-OS waits before declaring a route as invalid. If Cisco NX-OS does not receive route update information for a route before the timeout interval ends, Cisco NX-OS declares the route as invalid. The range is from 1 to any positive integer. The default is 180.

Holddown - time during which Cisco NX-OS ignores better route information for an invalid route. NX-OS waits for invalid route to become valid again, before using the new route. The range is from 0 to any positive integer. The default is 180.

garbage-collection - time from when Cisco NX-OS marks a route as invalid until Cisco NX-OS removes the route from the routing table. The range is from 1 to any positive integer. The default is 120.

switch(config-if)# ip rip metric-offset 10

Adds a value to the metric for every router received on this interface. The range is from 1 to 15. The default is 1.

switch(config-if)# ip rip route-filter route-map InputMap in

Specifies a route map to filter incoming or outgoing RIP updates

To Check

show run rip
show ip rip instance [instance-tag]?