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New Member

6500 link redundancy (eigrp)

Four 6500 connected to each other to form a full mesh.  Switches 4 and 7 is running eigrp.  A question came up, why didnt it have eigrp on SW 2 & 3 ?  Will it still be redundant if link between SW3 and SW4 is removed? If redundancy is working, SW3 should be able to find its way to SW4 via SW7 or SW2, yes?

The config looks:

SW4 eigrp

router eigrp 100

network 192.168.0.0

redistribute static

auto-summary

sh ip route static

S       x.x.242.48 [1/0] via x.x.186.10 (pointing to network outside of our LAN)

sh ip route summ

Route Source   Networks   Subnets    Overhead   Memory (bytes)

Connected        0           51         3672       7344

static               0           1           72         144

eigrp 400          1           6           504         1008

internal             3                                   6564

Total                 4           58         4248       15060

SW7 eigrp

router eigrp 100

network 192.168.0.0

auto-summary

sh ip route static

“EMPTY”

sh ip route sum

Route Source   Networks   Subnets     Overhead   Memory (bytes)

connected         0           51         3264       8160

static                0          0           0           0

eigrp 400         1           7           704         1280

internal              3                                   3540

Total                4           58         3968       12980

SW 2 and SW 3:

ip route

C 192.168.2.0 is directly connected, Vlan1

S* 0.0.0.0/0 [1/0] via 192.168.2.1 <--this is pointing to SW# 4

SW 2 and SW 3

sh ip route summ

Route Source   Networks   Subnets     Overhead   Memory (bytes)

connected         0           1           72         144

static               1           0           72         144

internal             1                                              2188

Total                 2           1           144         2476

Recently, the eigrp was configured to SW 2 and SW 3 as well, it included the “redistribute static” statement. The route for SW2 and SW3 now has the VLANs, 51 or so. Sent ping from a PC to VLAN1 IP of SW3, then link between SW3 and SW4 was disconnected, network connectivity went down for about 20secs, and ping came right back. Thought it was a success. All of a sudden, outside connectivity was lost. Ping within the LAN was successful, but no internet connection.

The eigrp on SW2 and SW3 was removed, and the internet connection came back up. The initial concern was that although there is physical redundancy in place, the other routes may not be known. Hence, eigrp configuration has been attempted for SW2 and SW3. Perhaps the “redistribute static” should have never been configured on SW2 and SW3, SW7 does not have the “redistribute static” statement anyway.

Without eigrp running on SW2 and SW3, does it still have redundancy? For what it’s worth, SW4 and SW7 are both VTP servers. With the current configs, does it still have redundancy? Link redundancy was never tested; it always has been assumed that it works. Later today, with it’s current config, the link redundancy will be tested.

Thoughts? Thanks.

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: 6500 link redundancy (eigrp)

Hello Adam,

yes the issue was caused by redistribute static within router eigrp process in SW2, SW3: they have a static default route pointing to SW4

>> S* 0.0.0.0/0 [1/0] via 192.168.2.1 <--this is pointing to SW# 4

This is redistributed into EIGRP causing internet traffic to blackhole. SW2 and SW3 were injecting route 0.0.0.0/0 in EIGRP.

SW2 and SW3 can have EIGRP enabled without red static.

On SW4 you should verify if you have ip default-network x.x.248.0 + network x.x.248.0 command under router eigrp to propagate a default route in EIGRP, if it is so you are fine and you can at the end remove the static default routes on SW2, SW3.

VTP is an unrelated matter, two VTP servers are recommended for redundancy.

Hope to help

Giuseppe

2 REPLIES
Hall of Fame Super Silver

Re: 6500 link redundancy (eigrp)

Hello Adam,

yes the issue was caused by redistribute static within router eigrp process in SW2, SW3: they have a static default route pointing to SW4

>> S* 0.0.0.0/0 [1/0] via 192.168.2.1 <--this is pointing to SW# 4

This is redistributed into EIGRP causing internet traffic to blackhole. SW2 and SW3 were injecting route 0.0.0.0/0 in EIGRP.

SW2 and SW3 can have EIGRP enabled without red static.

On SW4 you should verify if you have ip default-network x.x.248.0 + network x.x.248.0 command under router eigrp to propagate a default route in EIGRP, if it is so you are fine and you can at the end remove the static default routes on SW2, SW3.

VTP is an unrelated matter, two VTP servers are recommended for redundancy.

Hope to help

Giuseppe

New Member

Re: 6500 link redundancy (eigrp)

Hello G,

Thank you for your response. I will go ahead and try it again next week. As it is, the redundant link actually works when I finally tested it last night. I was just wondering if having the other two SW run eigrp would make it better.

Thanks again and will post the result next week.

Sent from Cisco Technical Support iPhone App

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