Multiple Routes on 3750X

[satish Chowdary]

Hi,

I have 3750X series 24 port switch with IP base license. I configured two MPLS lines on the switch and define the priority.

First MPLS line details 192.168.1.4

Second MPLS line details 192.168.1.252.

Please find the below configuration..

ip route 10.1.0.0 255.255.254.0 192.168.1.4 5

ip route 10.1.0.0 255.255.254.0 192.168.1.252 10

ip route 10.1.2.0 255.255.254.0 192.168.1.4 5

ip route 10.1.2.0 255.255.254.0 192.168.1.252 10

ip route 10.1.30.0 255.255.254.0 192.168.1.4 5

ip route 10.1.30.0 255.255.254.0 192.168.1.252 10

ip route 10.11.0.0 255.255.254.0 192.168.1.4 5

ip route 10.11.0.0 255.255.254.0 192.168.1.252 10

ip route 10.242.64.0 255.255.255.0 192.168.1.4 5

ip route 10.242.64.0 255.255.255.0 192.168.1.252 10

ip route 125.62.132.98 255.255.255.255 192.168.1.4

ip route 125.62.160.11 255.255.255.255 192.168.1.4

ip route 125.62.160.31 255.255.255.255 192.168.1.4

ip route 192.168.2.0 255.255.255.0 192.168.1.4

ip route 192.168.3.0 255.255.255.0 192.168.1.4

ip route 192.168.7.0 255.255.255.0 192.168.1.4

ip route 192.168.8.0 255.255.255.0 192.168.1.4

ip route 192.168.9.0 255.255.255.0 192.168.1.4

ip route 192.168.10.0 255.255.255.0 192.168.1.4

ip route 192.168.11.0 255.255.255.0 192.168.1.4

ip route 192.168.12.0 255.255.255.0 192.168.1.4

ip route 192.168.15.0 255.255.255.0 192.168.1.4

Aim is if first MPLS line is down, all traffic will pass through the send MPLS line. But it’s not happen.

Can you analyze the problem and guide me how to configure two routes for failover.

Regards,

Satish.

[mfurnival]

Hi,

Can you confirm what you mean by MPLS lines? Do you mean you have BGP configured on the switch?

What you have configured with those static routes is the following. Taking the example of:

ip route 10.1.0.0 255.255.254.0 192.168.1.4 5

ip route 10.1.0.0 255.255.254.0 192.168.1.252 10

The switch will forward traffic to 10.1.0.0 255.255.254.0 if the next hop 192.168.1.4 is reachable. If 192.168.1.4 is not reachable the switch will forward traffic to 10.1.0.0 255.255.254.0 to 192.168.1.252. If neither are reachable the packets will be dropped.

So the router does a recursive lookup for the next hop address and inserts the route if it is able to resolve the next hop.

Does that help?

[Richard Burts]

Based on 2 factors I would guess that the reference to MPLS lines means that 2 ports and perhaps 2 SVIs are configured to provide connectivity to a provider who is providing MPLS connectivity to remote sites and that BGP is not being used. But it would be good if Satish would confirm this.

- the use of static routes would not be necessary if BGP were being used.

- he indicates that the 3750 is running IP Base. I am not sure that BGP is supported in that image.

I see several things that could explain why the routing is not providing failover as Satish would like. First is some confusion about the addressing. Satish tells us that

First MPLS line details 192.168.1.4

Second MPLS line details 192.168.1.252.

When I first read this I assumed that Satish was indicating the subnet that was configured. Then I thought that perhaps these were the interface addresses. And the static routes make it look like these are the addresses of the provider. It would be helpful is Satish would provide more details about the configuration.

Then there are a number of routes configured using floating static routes. One example is this

ip route 10.1.0.0 255.255.254.0 192.168.1.4 5

ip route 10.1.0.0 255.255.254.0 192.168.1.252 10

I do not understand why both static routes are configured with administrative distance. A typical floating static route uses a normal static route paired with a static route specifying a higher administrative distance that will be used if the first route is removed from the routing table. But these specify distances of 5 and of 10.

There is an issue that comes up frequently when configuring floating static routes using Ethernet interfaces. The issue is how to know when to stop using the primary static route and start using the backup static route. In IOS typically the primary static route is removed from the routing table is the interface through which it goes to line protocol down. That works well for point to point serial interfaces. On these interfaces when you lose connectivity to the next hop device then the line protocol will usually change to down and the primary static route is removed. But on Ethernet interfaces the line protocol typically stays up even if you have lost connectivity to the next hop device. I suspect that is what is happening for Satish. The usual solution to this is to configure Object Tracking which will check on connectivity to the next hop device for the primary route and allow IOS to remove the primary static route is connectivity is lost.

The other issue that I see is that there are a series of static routes such as this which do not have a floating static route configured. So there can be no failover for these routes.

ip route 125.62.160.11 255.255.255.255 192.168.1.4

HTH

Rick