CEF load balancing in cat6k

[aviyoshi10]

Hello,

i have 2 X cat6k (1 for users and second for servers) connected to each other via 4 ethernet links point to point. routing protocol is ospf with max-path enabled.

there are about 100 useres that need to talk with 8 servers - so i have several different sessions.

i want to have load balancing via cef for all 4 links. - i am using the default cef configuration.

the problem is that i can see sessions only on 3 links, the 4th link is idle.

why?

how does the cef working on cat6k?

thanks,

Avi.

[Giuseppe Larosa]

Hello Avi,

>> the problem is that i can see sessions only on 3 links, the 4th link is idle.

IP OSPF cost may be manually set to an higher value

OR

the 4th link is in a different OSPF area

both can be checked with show ip ospf interface type x/y

OR

mazimum-paths is set to 3  (unlikely of course)

OR

4th link is in a different  routing table (VRF)

>> how does the cef working on cat6k?

(IP SA less meaningful two bits)  EXOR (IP DA less meaningful two bits) EXOR hash value   (this last can change at device reload)

Hope to help

Giuseppe

[aviyoshi10]

so if i have the server ip address to be consecutive, is this could be a problem with the hashing ?

[Giuseppe Larosa]

Hello Avi,

>> so if i have the server ip address to be consecutive

This shouldn't be a problem as the less meaningful bits changes

x.x.x.7   -> 11

x.x.x.8 ->   00

x.x.x.9 ->   01

x.x.x.10 ->    10

Hope to help

Giuseppe

[skarthic]

Do you see all 4 links in the routing table? If so you  can try "show mls cef exact-route " to check how the traffic would be forwarded as per 6k's hashing algorithm

[aviyoshi10]

Yes,

i do see the 4 links in the routing table.

the "show mls cef exact-route" load the traffic only over 3 links.