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Load balancing two T1's with a 2611

Is it possible to set up a 2611 router with two T1 CSU/DSU WICs to load balance between the two T1's, and if one should fail, to route all traffic over the one that is still up?



hi what routing protocol are you using? If you are using eigrp and since you have equal paths it will automatically load balance for you.

At the moment, I don't have the T1's, or the WIC's, but I'm looking to get a VoIP solution from Pingtone, and would like to find info on what can and can't be done with the router. The ideal solution would be to have the two T1's on the one 2611, and have them load balanced, the way I mentioned in my first pose, assuming the router is capable.

hi check out this link on the 2600

hope this helps

You can enable CEF for an effective load balancing. If you are running VOIP dont use per packet load sharing. Default mode of load sharing with CEF is per destination load balancing.

Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus

Do you have a sample configuration for bonding two T1's and using CEF

I don't think I can get to that page with my current login. What do I need to get access?

You need to have a contract with Cisco or purchased a cisco product (this may have changed)

Do you know what routing protocol u will be using. If you use statics then use cef like jshanky suggested.

Do you need help in purchasing equipment such as part number etc let me know

Some information on CEF since you cannot get to the links


The fast-switching mechanisms discussed in the previous sections all suffer the following drawbacks:

They are all traffic-driven, in that they depend on the reception of the first packet to populate the cache.

It is possible for caches to grow larger than routing tables, thus consuming significant amounts of memory.

Periodic aging of the cache entries can consume large amounts of CPU time if the cache is large.

Cache invalidation due to a route-flap relies on process-switching to re-populate the cache with valid entries.

On some platforms, the size of the cache may lead to cache entry churn if there are too many entries for the cache to support.

They are unable to do per-packet load-balancing from an interrupt level.

It is the inherent drawbacks to traditional demand-based caches that led to the development of Cisco Express Forwarding (CEF). The two main components of CEF are the Forwarding Information Base (FIB) and the adjacency table. Both tables are stored in DRAM memory.

The FIB table is used to make IP destination prefix-based forwarding decisions. It contains a mirror image of the information stored in the IP routing table. When routing or topology changes occur in the network, the IP routing table is updated, and those changes are reflected in the FIB. The FIB maintains next-hop address information based on the information in the IP routing table.

CEF also uses adjacency tables to prepend Layer 2 addressing information. The adjacency table maintains Layer 2 next-hop addresses for all FIB entries. The entries allow the Route/Switch Processor (RSP) to perform fast Layer 2 header rewrites when switching the packet from source interface to destination interface.

The adjacency table is populated as adjacencies are discovered. Each time an adjacency entry is created (for example, through the Address Resolution Protocol - ARP), a link-layer header for that adjacent node is precomputed and stored in the adjacency table. Once a route is determined, it points to a next hop and corresponding adjacency entry. That entry is then subsequently used for encapsulation during CEF switching of packets.

More information about CEF can be found at the CEF home page.

I think the only hardware I will need to get would be the WIC's, P/N WIC-1DSU-T1. I have a PIX 515-E Restricted coming, witch should arrive next week. Other than that, I think I'm pretty much set. I'll just need to figure out how to set up the 2611 and the PIX with the new configuration for the T1's.