ECMP static routes help

[vincehgov]

I have two routers, A and B, that are connected to each other via two FE links.

Each link has it's own subnet.  Each router also has its own loopback address.

Here is how it looks

   FA 1 -------------------   FA 1

A                                      B

   FA 2 -------------------   FA 2

A FA 1 : 10.1.1.1/30

A FA 2 : 10.2.1.1/30

A LO 0: 172.16.1.1/32

B FA 1: 10.1.1.2/30

B FA 2: 10.2.1.2/30

B LO 0: 172.16.1.2/32

I created 2 static routes on each router to get to the other router's loopback.

On router A:

ip route 172.16.1.2 255.255.255.255 fa 1

ip route 172.16.1.2 255.255.255.255 fa 2

On router B:

ip route 172.16.1.1 255.255.255.255 fa 1

ip route 172.16.1.1 255.255.255.255 fa 2

I still cannot ping the loopback from the other router.  When I shut down one of the ports, it works.  I can ping each of the physical ports fine.

Is this not supported?

[cadet alain · Accepted solution]

Hi,

is it working when you configure the static routes pointing to next-hop instead of outgoing interface ?

Can you also try with network routes instead of host routes.

Regards.

Alain.

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[vincehgov]

Hi Alain,

I will try with next-hop address when I get to the office.  What do you mean when you say network routes?  Like create a bigger subnet to try instead of the /32?

Vince

[cadet alain]

Hi,

yes I mean  ip route 172.16.1.0 255.255.255.0

Regards.

Alain.

Don't forget to rate helpful posts.

[vincehgov]

Thank you.  Setting the next hop to the ip address rather than out the interface worked. 

Do you have an explanation of why that didn't work before? 

[vincehgov]

I mean, why setting the next hop to the interface didn't work.

[cadet alain]

Hi,

I labbed it up and here is what is happening when using the outgoing interface in both static routes:

r1(config)#do p 172.16.1.2 so lo0

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.16.1.2, timeout is 2 seconds:

Packet sent with a source address of 172.16.1.1

.....

Success rate is 0 percent (0/5)

r1(config)#do debug arp

ARP packet debugging is on

r1(config)#do p 172.16.1.2 so lo0

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.16.1.2, timeout is 2 seconds:

Packet sent with a source address of 172.16.1.1

*Mar  1 00:08:53.203: IP ARP: sent req src 10.2.1.1 c200.0a8c.0001,

                 dst 172.16.1.2 0000.0000.0000 FastEthernet0/1

*Mar  1 00:08:53.435: IP ARP rep filtered src 172.16.1.2 c201.0a8c.0001, dst 10.2.1.1 c200.0a8c.0001 wrong cable, interface FastEthernet0/1.

*Mar  1 00:08:55.199: IP ARP: sent req src 10.1.1.1 c200.0a8c.0000,

                 dst 172.16.1.2 0000.0000.0000 FastEthernet0/0

*Mar  1 00:08:55.371: IP ARP rep filtered src 172.16.1.2 c201.0a8c.0000, dst 10.1.1.1 c200.0a8c.0000 wrong cable, interface FastEthernet0/0.

*Mar  1 00:08:57.199: IP ARP: sent req src 10.2.1.1 c200.0a8c.0001,

                 dst 172.16.1.2 0000.0000.0000 FastEthernet0/1

*Mar  1 00:08:57.347: IP ARP rep filtered src 172.16.1.2 c201.0a8c.0001, dst 10.2.1.1 c200.0a8c.0001 wrong cable, interface FastEthernet0/1.

*Mar  1 00:08:59.199: IP ARP: sent req src 10.1.1.1 c200.0a8c.0000,

                 dst 172.16.1.2 0000.0000.0000 FastEthernet0/0

*Mar  1 00:08:59.267: IP ARP rep filtered src 172.16.1.2 c201.0a8c.0000, dst 10.1.1.1 c200.0a8c.0000 wrong cable, interface FastEthernet0/0.

*Mar  1 00:09:01.199: IP ARP: sent req src 10.2.1.1 c200.0a8c.0001,

                 dst 172.16.1.2 0000.0000.0000 FastEthernet0/1

*Mar  1 00:09:01.327: IP ARP rep filtered src 172.16.1.2 c201.0a8c.0001, dst 10.2.1.1 c200.0a8c.0001 wrong cable, interface FastEthernet0/1.

Success rate is 0 percent (0/5)

r1(config)#do sh arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  10.1.1.1                -   c200.0a8c.0000  ARPA   FastEthernet0/0

Internet  10.2.1.1                -   c200.0a8c.0001  ARPA   FastEthernet0/1

Regards.

Alain.

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