eigrp offset-list

2013.04.13

offset lists are a tool to manipulate paths for eigrp routes.  in my topology, 4.4.4.4/32, 4.4.4.5/32, and 4.4.4.6/32 are loopbacks on r4.  fa1/0 has a delay of 10000 and fa2/0 has a delay of 15000 on both r2 and r3.  without any any changes, successor and feasible successor to r4 show up in the topology table but fa1/0 is preferred.

i want to make 4.4.4.5/32 and 4.4.4.6/32 prefer fa2/0 instead.  i found it’d be easier to understand outbound metric changes, since the router announcing the routes is the authority on which path to take.

offsetlistopology
routing table:

r2#sh ip route 4.4.4.5   
Routing entry for 4.4.4.5/32
  Known via "eigrp 1", distance 90, metric 2946560, type internal
  Redistributing via eigrp 1
  Last update from 10.23.23.3 on FastEthernet1/0, 00:00:41 ago
  Routing Descriptor Blocks:
  * 10.23.23.3, from 10.23.23.3, 00:00:41 ago, via FastEthernet1/0
      Route metric is 2946560, traffic share count is 1
      Total delay is 105100 microseconds, minimum bandwidth is 10000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2

topology:

r2#sh ip eigrp top 4.4.4.5/32
EIGRP-IPv4 Topology Entry for AS(1)/ID(2.2.2.2) for 4.4.4.5/32
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2903808
  Descriptor Blocks:
  10.23.23.3 (FastEthernet1/0), from 10.23.23.3, Send flag is 0x0
      Composite metric is (2946560/2713600), route is Internal
      Vector metric:
        Minimum bandwidth is 10000 Kbit
        Total delay is 105100 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 2
        Originating router is 4.4.4.4
  10.23.23.131 (FastEthernet2/0), from 10.23.23.131, Send flag is 0x0
      Composite metric is (6741248/2713600), route is Internal
      Vector metric:
        Minimum bandwidth is 12004 Kbit
        Total delay is 255000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 2
        Originating router is 4.4.4.4

from r3, i can create an acl for routes i want to offset:

r3#sh run | s access-list
access-list 45 permit 4.4.4.5
access-list 45 permit 4.4.4.6

i use the offset-list to make fa1/0 less desirable than fa2/0:

r3#sh run | sec router eigrp 1
router eigrp 1
 network 3.3.3.3 0.0.0.0
 network 10.23.23.0 0.0.0.255
 network 10.34.34.0 0.0.0.255
 redistribute static
 offset-list 45 out 10000000 FastEthernet1/0  < ---------
 eigrp router-id 3.3.3.3

net result is that it adds 10000000 to the existing metric on fa1/0:

r3#sh ip prot
*** IP Routing is NSF aware ***

Routing Protocol is "eigrp 1"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Outgoing routes in FastEthernet1/0 will have 10000000 added to metric if on list 45  < ---------
  Default networks flagged in outgoing updates
  Default networks accepted from incoming updates
  Redistributing: static
! dropped irrelevant

back on r2, i should see the path to 4.4.4.5/32 via fa2/0:

r2#sh ip route 4.4.4.5       
Routing entry for 4.4.4.5/32
  Known via "eigrp 1", distance 90, metric 6741248, type internal
  Redistributing via eigrp 1
  Last update from 10.23.23.131 on FastEthernet2/0, 00:00:06 ago
  Routing Descriptor Blocks:
  * 10.23.23.131, from 10.23.23.131, 00:00:06 ago, via FastEthernet2/0
      Route metric is 6741248, traffic share count is 1
      Total delay is 255000 microseconds, minimum bandwidth is 12004 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2

both successor and feasible successor should still be in the topology table on r2:

r2#sh ip eigrp top 4.4.4.5/32
EIGRP-IPv4 Topology Entry for AS(1)/ID(2.2.2.2) for 4.4.4.5/32
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2903808
  Descriptor Blocks:
  10.23.23.131 (FastEthernet2/0), from 10.23.23.131, Send flag is 0x0
      Composite metric is (6741248/2713600), route is Internal
      Vector metric:
        Minimum bandwidth is 12004 Kbit
        Total delay is 255000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 2
        Originating router is 4.4.4.4
  10.23.23.3 (FastEthernet1/0), from 10.23.23.3, Send flag is 0x0
      Composite metric is (12946560/12713600), route is Internal
      Vector metric:
        Minimum bandwidth is 10000 Kbit
        Total delay is 495725 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 2
        Originating router is 4.4.4.4

verification from r1:

r1#traceroute 4.4.4.4
Type escape sequence to abort.
Tracing the route to 4.4.4.4
VRF info: (vrf in name/id, vrf out name/id)
  1 10.12.12.2 16 msec 16 msec 24 msec
  2 10.23.23.3 40 msec 44 msec 44 msec  < ---------
  3 10.34.34.4 72 msec *  56 msec
r1#traceroute 4.4.4.5
Type escape sequence to abort.
Tracing the route to 4.4.4.5
VRF info: (vrf in name/id, vrf out name/id)
  1 10.12.12.2 20 msec 20 msec 20 msec
  2 10.23.23.131 44 msec 44 msec 40 msec  <---------
  3 10.34.34.4 64 msec *  60 msec

i’ll use this at work for some traffic engineering on datacenter-datacenter links.  i wanted to send some non-critical traffic down a slower link to get some better utilization across both links. we’re paying for unlimited transit, so don’t want one path to sit idle.

Categories : geek
trackback

Leave a comment