Multihoming with Cisco 3640 router questions

Posted on 2008-10-29
Last Modified: 2010-04-17
I currently have a Cisco 3640 router and 3 T1's in a multilink PPP configuration from my primary ISP.  I recently added 2 T1's also in a multilink PPP configuration from a secondary provider.  I obtained an ASN and we configured BGP to run over the MLPPP interface with both providers.  I am receiving default routes from both ISP's

I have 2 class C address blocks and 2 partial address blocks from the primary ISP.  I want to configure the router to send traffic on the 2 Class C blocks thru the secondary provider upon failure of the first.
The secondary provider is configured to allow me to announce the 2 class C's thru their network.

The first thing I am not sure of, is if the Cisco 3640 router is capable of doing this efficiently, because if it is not, I need to figure out what router (that I can afford thru ebay ;) ) I would need.

If this router is capable, I am not sure how to configure the BGP session to do this.

I would also appreciate an explanation of any code because while I understand basic cisco programming, we are entering an area where I don't understand the commands and what they specifically do internally.  I'd like to understand that.

Thank you for your time!
Question by:USGRobocoder
  • 3
LVL 12

Expert Comment

ID: 22836472
I do the same thing there but with 7200's..

two seperate links from ISP's coming into 2 x 7200's.. running BGP for all our class C's.. we run OSPF internally as well, and have setup HSRP with iBGP between the two 7200's for failover, so that we have a 'primary' ISP and upon failure we cut over to our secondary ISP..

it all depends on your ISP's though and how they configure / want to configure you.. you'd probably have to use AS prepending to prioritize your paths.. or perhaps communities preferencing.. depending again on your ISP..

as for the 3600's.. we havent had them for many many years.. i remember we used to run BGP and OSPF on them, but had a lot of issues with bgp tables filling the memory on them.. id be recommending upgrading to better routers..

Good luck with it !

Author Comment

ID: 22836529
Thank you for the input, however, I may not have asked the question correctly (my first time using this service).  I am looking how to write the code to do the multihoming/failover.

LVL 12

Accepted Solution

Steve earned 500 total points
ID: 22853613
To enable Hot Standby Routing Protocol, you need two Layer 3 switches or routers with routing enabled. Set up a primary device, assign it a "real" IP address, and configure HSRP on this device with a virtual IP in the same network segment as the "real" IP. Configure your secondary device with a "real" IP address, then configure HSRP on this device using the virtual IP configured on the primary. Make certain each L3 router has the real IP of the other inside the HSRP configuration. Set up your priorities on each device, then attach one NIC from each server to each switch. You'll need something to create network teams on your servers to ensure redundancy, but we have this type of setup deployed several times over.

Assuming that each router has an ISP assigned IP address on the outside interface and a direct connection to the ISP, then simply enable BGP on both routers, given the information provided by the ISP. I can assume also that they will only give you a default route. You simply do not have the horsepower to run full BGP route tables on 3600's though.. (Hence my statement to upgrade to more powerful routers)

On the inside, it won't matter how they get their default route. The issue you will have is with your HSRP and the "track" command. You need to track the interface events to determine which router should become primary.

Have you looked into GLBP?

so some code for your primary router for example.. (you'll have to modify of course.)..
the setup is the same for the other router except you'd have to modify IP's to match that ISP/router and change community to say :4000 instead of :8000 to work as secondary..

router bgp 64512                              <- Your AS Number
 no synchronization
 bgp log-neighbor-changes
 network x.x.x.0                              <- Your Class C
 neighbor <IP of other 3640> remote-as 64512
 neighbor <IP of other 3640> send-community both
 neighbor <IP of other 3640> soft-reconfiguration inbound
 neighbor <ISP Side IP> remote-as 9999   <- AS Number of ISP
 neighbor <ISP Side IP>  send-community both
 neighbor <ISP Side IP>  soft-reconfiguration inbound
 neighbor <ISP Side IP>  route-map HSRP-IN in
 neighbor <ISP Side IP>  route-map HSRP-OUT out
 no auto-summary
route-map HSRP-OUT permit 10
 match as-path 10
 set community <isp AS Number>:8000  <- This is using communities to set preference, but you can also look at using as-precedence.
route-map HSRP-IN permit 10
 set local-preference 100

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LVL 12

Expert Comment

ID: 22853631
Then on your interfaces you have something like ;

interface GigabitEthernet0/1
 <snip all normal stuff>
 standby 10 ip <Virtual IP address within same subnet>
 standby 10 priority 150
 standby 10 preempt

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