Offset-List EIGRP


EIGRP Load Balancing

Let’s do some more load balancing and concentrate on 100.100.100.0 network which is behind R1

  • R7#sh ip route | be 100.100.100.0
  • D       100.100.100.0
  • [90/2177536] via 150.100.221.6, 01:01:55, FastEthernet0/1
  • [90/2177536] via 150.100.221.5, 01:01:55, FastEthernet0/1
  • [90/2177536] via 150.100.220.6, 01:01:55, FastEthernet0/0
  • [90/2177536] via 150.100.220.5, 01:01:55, FastEthernet0/0
  • D       100.100.200.0 [90/2172416] via 150.100.78.8, 01:01:32, Serial0/0
  • D       100.100.250.0
  • [90/2174976] via 150.100.221.6, 01:01:55, FastEthernet0/1
  • [90/2174976] via 150.100.220.6, 01:01:55, FastEthernet0/0
  • 200.0.0.0/32 is subnetted, 8 subnets
  • D       200.0.0.8 [90/2297856] via 150.100.78.8, 01:01:32, Serial0/0
  • D       200.0.0.9 [90/2300416] via 150.100.221.6, 01:01:55, F
  • R7(config)#do sh ip eigrp top  | be 100.100.100.0
  • P 100.100.100.0/24, 4 successors, FD is 2177536
  •         via 150.100.220.5 (2177536/2174976), FastEthernet0/0
  •         via 150.100.220.6 (2177536/2174976), FastEthernet0/0
  •         via 150.100.221.5 (2177536/2174976), FastEthernet0/1
  •         via 150.100.221.6 (2177536/2174976), FastEthernet0/1
  • P 150.100.100.0/24, 2 successors, FD is 2172416
  •         via 150.100.220.6 (2172416/2169856), FastEthernet0/0
  •         via 150.100.221.6 (2172416/2169856), FastEthernet0/1
  • P 150.100.81.0/24, 1 successors, FD is 2172416
  • We have 4 paths available to us
  •  
  • So let’s change the bandwidth for one of the outgoing interfaces :
  • R7(config)#int fa 0/0
  • R7(config-if)#band
  • R7(config-if)#bandwidth 100
  • R7(config-if)#exi
  • R7(config)#do sh int fa 0/0
  • FastEthernet0/0 is up, line protocol is up
  •   Hardware is Gt96k FE, address is c201.0aa8.0000 (bia c201.0aa8.0000)
  •   Internet address is 150.100.220.7/24
  •   MTU 1500 bytes, BW 100 Kbit, DLY 100 usec,
  •      reliability 255/255, txload 1/255, rxload 1/255
  •   Encapsulation ARPA, loopback not set
  •   Keepalive set (10 sec)
  • R7(config)#do sh int fa 0/1
  • FastEthernet0/1 is up, line protocol is up
  •   Hardware is Gt96k FE, address is c201.0aa8.0001 (bia c201.0aa8.0001)
  •   Internet address is 150.100.221.7/24
  •   MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
  •      reliability 255/255, txload 1/255, rxload 1/255
  •   Encapsulation ARPA, loopback not set
  • As we can see fa 0/1 has not been changed and we get :
  • R7(config)#do sh ip eigrp top | be 100.100.100.0
  • P 100.100.100.0/24, 2 successors, FD is 2177536
  •         via 150.100.220.5 (26119680/2174976), FastEthernet0/0
  •         via 150.100.221.5 (2177536/2174976), FastEthernet0/1
  •         via 150.100.221.6 (2177536/2174976), FastEthernet0/1
  •         via 150.100.220.6 (26119680/2174976), FastEthernet0/0
  • R7(config)#do sh ip route eig | be 100.100.100.0
  • D       100.100.100.0
  •            [90/2177536] via 150.100.221.6, 00:02:23, FastEthernet0/1
  •            [90/2177536] via 150.100.221.5, 00:02:23, FastEthernet0/1
  • D       100.100.200.0 [90/2172416] via 150.100.78.8, 01:08:49, Serial0/0
  • D       100.100.250.0
  •            [90/2174976] via 150.100.221.6, 00:02:23, FastEthernet0/1
  •      200.0.0.0/32 is subnetted, 8 subnets
  • So now we have a requirement to do load balancing between these two interfaces but we are not allowed to use the variance command , how do we so this ?
  • We go back to a topology table where and check the metric values
  •         via 150.100.220.5 (26119680/2174976), FastEthernet0/0
  •         via 150.100.221.5 (2177536/2174976), FastEthernet0/1
  •         via 150.100.221.6 (2177536/2174976), FastEthernet0/1
  •         via 150.100.220.6 (26119680/2174976), FastEthernet0/0
  • we subtract 26119680 – 2177536 = 23942144 and we apply an offset-list
  • R7(config-router)#offset-list 0 in 23942144 fastEthernet 0/1
  • R7(config-if)#do sh ip eigrp top | be 100.100.100.0
  • P 100.100.100.0/24, 4 successors, FD is 26119680
  •         via 150.100.220.5 (26119680/2174976), FastEthernet0/0
  •         via 150.100.220.6 (26119680/2174976), FastEthernet0/0
  •         via 150.100.221.5 (26119680/26117120), FastEthernet0/1
  •         via 150.100.221.6 (26119680/26117120), FastEthernet0/1
  • now we see the metric being equal J
Advertisements

About ccie4all
Hello, and welcome to the first post of my CCIE blog This blog has got one simple goal and that is to improve our skills in Cisco Networking field so we can become best engineers on a job market. Wordpress Blog https://ccie4all.wordpress.com/ information about the changes made to Gns3 BGP , MPLS and R&S CCIE labs. In order to access and download all provided materials and receive important updates from Gns3 BGP , MPLS and R&S CCIE labs under GNS3 tab in the main header please go ahead and subscribe to https://ccie4all.wordpress.com/ ! All other posts have not been affected and can be accessed at any given time. Enjoy ! Tom

7 Responses to Offset-List EIGRP

  1. suman says:

    Thanx it is a nice document.Pls help me to clear difference between distance & offset-list command in eigrp.

  2. suman says:

    what is function of Offset-List EIGRP command.what is difference between delay,distance & dalay command in eigrp.

  3. ccie4all says:

    hi Suman
    In my opinion changing the interface delay parameter is the best method of influencing path selection for eigrp because changes are propagated to all downstream routers.
    Be careful however when changing the new delay cause you do not want to increase the delay to a point where the router no longer see another route as a feasible successor.

    An offset-list is the preferred method when you only want to influence a particular path being advertised.

    Administrative distance is less ideal as It can increase the potential for routing loops.Administrative distance is not propagated to other routers. Routing protocols rely on the fact that all routers choose the same path given the same set of parameters. Different parameters on a single router can lead to routing loops.

    Distance i would presonally use only when doing redistribution between two protocols and needed to change parameters for a particular route.
    Offset list looks much more clearer with RIP cause of its 15hops metric
    Delay and possibly bandwidth are the best methods to influence EIGRP path decision.

    but for the lab exam you need to know all of them cause you never know what they’ll ask you to do

    • suman says:

      Hi Tom
      Thanks a lot.If i use offset-list to modify a particular path in eigrp will it propagate to all downstream routers?

  4. ccie4all says:

    hi Suman
    —-r2—-
    | |
    r1—- —–10.1.3.0
    | |
    —-r3—-
    well , imagine above network setup. At the moment R1 is load balancing between R2 and R3 to reach 10.1.3.0. We can apply below configuration let’s say on R3

    access-list 50 permit 10.1.3.0 0.0.0.255
    router eigrp 1
    offset-list 50 out 40 FastEthernet0/0

    R3 fa0/0 goes towards R1. This way when you issue
    sh ip eig top 10.1.3.0 255.255.255.0
    on R1 you will see that the composite metric for 10.1.3.0 network has increased by 40 (as specified in the offset list) and R3 now becomes a backup path to reach 10.1.3.0.
    R2 does not get affected by it as it is directly connected to 10.1.3.0 however when you issue the same command on R2
    sh ip eig top 10.1.3.0 255.255.255.0
    you will notice that the backup metric for 10.1.3.0 network via R3 has also increased
    so the answer is , yes offset-list does indeed affect an entire topology and other devices will recalculate their paths to reach certain networks.

    • suman says:

      Thanks u

      • suman says:

        Hi hope u r well, pls help me in explaing default-information-originate command of ospf ,why it is use when lsa 5 & lsa 4 is there.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: