We are considering a dual router branch office design and wanted to hear from anyone who has done this already, and what their general experience was (eg. âwent great but watch out forâ¦â).
We have dual 6509-Es in our HQ anchoring T1s and T3s for ~20 branches. Our largest branch currently has a single 3845 anchoring dual T3s (one to each 6509) and 6 multilinked T1s (for backup).
We have a business requirement to make this office âhighly redundantâ and one of the only single-points-of-failure left is the 3845.
Our thought is to add a second 3845, split the T3s between them, and cross connect them with two branch 4510s acting as backbones. Redundancy achieved through L3 OSPF routing, not STP, HSRP, etc., allowing us to use all of our bandwidth with quick failover.
* We have all devices in Area 0. Yes we know that's not ideal.
* We use Cisco phones at the branches connecting to call managers in HQ.
* 3 voice PRIs would be split across both routers.
* Internal switches are all L3 routing OSPF with connections to both cores.
I saw some useful information in both the High Availability Campus Network Design and the Enterprise Branch Office Design, but nothing beats what you can learn from the experience of others.
Any suggestions or comments based on the experience of others?
Using /30s works fine, or we've found letting the WAN edge peer with the LAN on a dedicated subnet works well too. The latter saves one less subnet per occurance within the topology.
If you have dual LAN routers, also best, if possible, to have dual links from each WAN router. That way you don't lose half your WAN bandwidth with loss of a LAN router.
No, don't believe GLBP has an advantage over OSPF if you have a LAN router in front of the WAN routers and if you have equal cost paths. If you need to support unequal cost paths, believe then GLBP could help. Or, again, in situations where you don't have an internal LAN router to provide ECMP.
With regard to remote trouble shooting, you can also wire one router's aux port to the other's console port and use reverse telnet.
With multiple paths, you can also perform IOS reloads during business hours. (Best to cost the links such that the target router stop forwarding traffic before doing the reload.)