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Failover from T1 to Frame Relay (C2600)

Posted on 2004-08-02
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Last Modified: 2010-04-17
I'm a bit confused about a failover and was hoping to clear up some questions..

I've got Router B (Routing protocol is RIP) with two serial interfaces
Serial 0/0 - T1
Serial 0/1 - Frame

My routing setup on Router B is:
ip route 0.0.0.0 0.0.0.0 <T1 next-hop IP>
ip route 0.0.0.0 0.0.0.0 <Frame next-hop IP> 125

Now, on Router A (also using RIP), I've got a route-map that routes traffic from LAN of Router A (source) with a destination of LAN on Router B over the T1 line.  
Route-map X permit 10
Match address 112
Match interface (T1 interface)
Set ip next-hop (T1 next-hop)

I pulled the T1 line from CSU/DSU from Router B and we lost connectivity with Router A's LAN.  If that because Router A is forced to route traffic over the T1 due to my route-map policy?  Why did the traffic not begin routing over the frame?

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Question by:dgroscost
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by:lrmoore
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Your route-map specifies next hop, it does not allow for the failure of that interface and provide for an alternate path.
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by:dgroscost
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How would I enable failover then?

Match interface (T1 interface) (Frame interface)
Set ip next-hop (T1 next-hop IP) (Frame next-hop IP)

?
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by:lrmoore
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Can you describe your setup a little better?

LANA ----RtrA      T1------------T1      RtrB --- LANB
                 \   frame -----------frame /

If you are using any dynamic routing protocol (you mentioned RIP), then the routes are chosen automatically. What are you hoping to accomplish with the route-map?
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by:dgroscost
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You have it exactly.  We have a T1 line as well as a Frame Relay drop in both locations.  

Router A (x.x.100.1 - T1 line)
Router A (x.x.60.2 - Frame Relay)

Router B (x.x.100.2 - T1 line)
Router B (x.x.60.4 - Frame Relay)

I want to route all traffic into Router B to go over the T1 line (100.1 <-> 100.2)

If, for some reason, the T1 line drops, I'd like for the Frame Relay line to take over connectivity. (60.2 <-> 60.4)

This was the reason I created a route-map -- to force ALL traffic over the T1 line.  But it seems to be interfering with the failover.

I am using RIP, however, I wasn't sure if it would automatically failover without adding floating static routes on Router B.


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by:lrmoore
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Rip uses simple hop-count, so may not be your answer.
OSPF and EIGRP are better suited to determine the best route based on a variety of metrics.
Simple floating statics are the best way to direct traffic, but you have to do both ends which is not conveninient if you have multiple sites.
I would definately look at a more robust dynamic routing protocl like OSPF to make the routing decisions for me instead of trying to force it with a route map.
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by:dgroscost
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RIP is probably the only option available to me at this time.  Once I am more familiar with routing protocols, I'll probably switch over to either EIGRP or OSPF.  

For now, should I set up a route-map policy on Router B?  Or would I need to add a floating route on Router A to switch over to Frame if the T1 drops?  

Can't I just add two floating routes (with cost 125, 130) with the T1 line being 125 and the Frame being 130 on both Routers?

There has to be an easy way of doing this...
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by:mikebernhardt
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You may find it easier to use EIGRP if you're converting from RIP, because it is configured similarly. Only one additional thing to do: On the serial interfaces, just configure a bandwidth statement that gives the actual bandwidth of the serial link in kbps. As long as the frame relay bandwidth is set lower than the T1 on both sides, EIGRP (or OSPF) will ALWAYS choose the T1 if it's available.

The other advantage of EIGRP or OSPF over RIP is that they will failover much faster- in seconds, not minutes.
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by:dgroscost
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I agree with both of you on switching over to EIGRP or OSPF, but right now with 7 sites and a mixture of Bay ASN + Cisco, it's not exactly the easiest thing in the world to do.  I'm slowly removing Bay from the picture, and once I get to that point, I would like to introduce EIGRP or OSPF.  For the time being, am I simply out of options due to using RIP, or can I some how get this to work with a mixture of floating routes & route-maps?

I don't want to load balance - 100% over the T1 line unless it fails, then the frame will need to take over (until the T1 connectivity is restored.)
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by:mikebernhardt
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Check this out
http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/products_configuration_guide_chapter09186a00800ca569.html#4653

I've never used it, but it appears to let you do the same thing as discussed for EIGRP: You can specify an interface and tell RIP to add some number of hops to any routes learned (or broadcast) on that interface. By putting that on the frame relay interface on both sides, you would make routes through that interface less preferable.
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by:dgroscost
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If I remove RIP from Router B, is this scenario possible?
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by:mikebernhardt
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No, the whole point is to let a dynamic routing protocol make the determination about what route to take. If you remove RIP from one side it will break.

The routing is already there. Just set your offsets, remove your static routes, and let 'er, well, RIP!

For default route, the best thing is to put the static default on the router that actually has the internet gateway and redistribute that into RIP.
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by:dgroscost
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The problem is that I need to enforce route-map policies because I want traffic to flow over certain links throughout the sites.  For example, two of the seven sites, I have the traffic flowing over the Frame Relay link rather than the Backup PTP T1.  However, for the case mentioned above, I have traffic flowing over the T1 but would like Frame Relay to be there for as a backup.  will EIGRP or OSPF be able to support such routing policies and offer some sort of failure backup measures?

Thanks
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by:lrmoore
lrmoore earned 250 total points
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Yes. Simply set the "bandwidth" statement on the circuit that you want to take priority with a higher number than the other circuit.

example:

Interface serial 0/0.12
 description frame-relay PVC
 bandwidth 384
 ip address 192.168.122.13 255.255.255.252

Interface serial 0/1
 description PTP T1
 bandwidth 1544
 ip address 192.168.111.13 255.255.255.252

router ospf 202
 network 192.168.111.13 0.0.0.0 area 0
 network 192.168.122.13 0.0.0.0 area 0
 redistribute connected subnets
OR
router eigrp 202
 network 192.168.111.0
 network 192.168.222.0
 no auto-summary


This configuration will always take the PTPT1 unless it's down.
Reverse the bandwidth statements, and you reverse the priority of the interfaces.


 
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by:mikebernhardt
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Or in RIP, do the following using the above interface configuration:

router rip
 network 192.168.111.0
 network 192.168.222.0
 offset-list 15 in 1 serial 0/0.12

access-list 15 permit any

This has the effect of adding 1 hop to the metric of all routes learned from serial 0/0.12, which should be 1 hop more than what's learned over the T1 (or vice versa when necessary). You may need to change the number of hops added depending on your exact topology.
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by:dgroscost
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Will this need to be done on both connecting routers?

I don't want it to interfere with connectivity to the other Frame connections.  I'm not using subinterfaces, just Serial 3/1 and broadcasting the frame IPs from there.

Would I have the access list specify that subnet only?  That way the deny statement would ignore each of the other subnets (frame connections)?

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by:mikebernhardt
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You can specify any interface you want to apply the offset-list to, and any routes you want. Any routes not listed would be unchanged.

Exactly how you implement it really depends on your exact topology. When you set an inbound list, you are telling the router which link to send traffic OUT on, because the list controls inbound routes, not inbound traffic. When you set an outbound list, you are telling the router to advertise the route out differently depending on the link. This will affect INBOUND traffic because the attached router will pick the better route.

So you probably want to put it on every router, but if you're trying to specify which routes you adjust, the access list will have to be different on every router. I suggested "any" because it covers any route, but only affects the metric on the interface you specify. Other interfaces are unaffected.

When you set an inbound list, the extra hop you added will be advertised out to the next router, so a route that arrived with a metric of 1 will leave with 3, not 2. Remember that you only have 15 hops to play with in RIP. If you add hops everywhere you may run out. If your 7 sites are more or less in a star topology you should be fine. If they're in a string you may have a problem. That's one reason (of many) why EIGRP or OSPF are so much better than RIP.
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by:dgroscost
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This sounds like it would work in a less complication, smaller environment.  I'm tempted now if I should start a new thread - support on converting from RIP to EIGRP.  Unless you're up for a challenge? :)
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mikebernhardt earned 250 total points
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Well, lrmoore and both I think it's a good idea to convert- but you'll still deal with the same design issues in a way. You still need to think about how you want your traffic to flow. An offset list is way easier than the policy routing you were trying to do!

Your original question was on how to have automatic failover between 2 serial links running rip, with one primary and the other backup. What I suggested would add 1 hop to any routes arriving on the backup link but do nothing to any of the other links, whatever they are. That would give you what you asked for. Unless your network really is a string of 7 routers in a row, you shouldn't have a problem using RIP and an offset list for now.

That will give you your failover while you plan out your EIGRP conversion.
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by:dgroscost
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Here's what I did:

I set up an offset for IN and OUT of Serial 0/1 (Frame) adding +1 offset.  I did this on the Router B end.

Traceroute's show constant T1 routing on both ends.  I'll try shutting down the T1 interface tonight from Router A and see the results.

Thanks - I'll keep you posted!
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by:mikebernhardt
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That should work, good luck!
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