Routing between Dual T1 circuits 1

[marcvu]

Hi,

Currently I have a cisco 3600 router doing routing between 2 different T1 circuits. The problem I am having is that connection to certain sites would not work i.e FTP or SSL sites. From what I am seeing is that the router doesnt keep a persistant route within the circuit. Routes are getting lost or confused between the 2 circuits. Any ideas or help would be great.

Thanks

Marc

 

[wybnormal]

If you are running some type of routing protocol like EIRGP or OSPF, it's probably loading balancing an equal cost path.. i.e. both circuits are costing the same so it's sending one packet here and the other there in a round robin effect.

There are many ways to do this.. you could add static routes with different costing on it, change the costing in OSPF, use policy routing to force certain packets or data streams to use one or the other pipe and so on.

Here is a link for setting prefered routes in EIGRP

http://www.cisco.com/warp/public/103/14.shtml

Here is OSPF costing

http://www.cisco.com/warp/public/104/2.html#2.1

Here is a link on how load balancing works

http://www.cisco.com/warp/public/105/46.html

Hope this helps

Mike S
"Diplomacy; the art of saying 'nice doggie' till you can find a rock" Wynn Catlin

 

[marcvu]

Thanks....Let me give it a try.

 

[talisker]

Actually, it sounds like your router may be doing "per-packet" load-balancing (sends packet 1 via the first path & packet two via the sencond path) instead of "per-destination" load-balancing (sends all packets going to the same destination via the same path).

Check if you have route-caching turned on:
sh ip int

You should see a line that says: IP Fast switching is enabled

If it is disabled, then you need the following global config command:

int fastethernet0/1
ip route-cache

You need to do this regardless of whether you use RIP, OSPF or EIGRP. Per-packet and destination load-balancing is independent of the routing protocol. B-)

 

[marcvu]

Hey Talisker,

Tried to do the per-destination configuration but still no luck with my connections. Anything else you can suggest?

Marc

 

[talisker]

I'm not clear as to your Internet connection - are you saying you have two T1 P2P connections to your ISP?

Have you done traceroutes to confirm that packets are taking different routes to the web/ftp sites? This will also tell you where the packets are being dropped (at your router or the ISPs router.

Also, try using extended ping with the DF bit set and then with it not set to see if there's an MTU size mismatch somewhere.

 

[jeter]

You guys think that PPP multilink may be the answer here?
Its worked for me in the past. Good Luck !!! #-) J.Fisher CCNA
Jeter@LasVegas.com

 

[marcvu]

Jeter,

Do you have any docs about how to do multilink on T1 circuits?

Marc