standby route between two Catalyst switches

[broow]

we have two 6500's on two campus separated by a mile with aerial fiber connecting the switches. We have contracted with a local provider to supply a redundant fiber path. We pay a monthly fee to have the fiber and will pay an additional fee if we have to use the fiber. How can I configure the switches to have the aerial fiber active and the dark fiber in standby only to be active in the event the aerial fiber is damaged? Each switch is in its own vtp domain. We have vlan 204 on each switch. 172.28.1.1 on one switch and 172.28.1.2 on the other switch to route between the switches.

[jon_marshall]

If the interconnection is L2 then you can allow STP to block the dark fiber link and only use it if the other link fails. You may need to modify STP port costs etc. to make sure the right link is used in normal operation.
If the interconnection is L3 then it depends on how you exchange routes. If it is just statics then use a floating static for the dark fiber link eg.

ip route <network> <mask> <next-hop> 200 <--- note the 200, this is very important.


Jon

[broow]

thanks for the good feedback.

I added another vlan 205 for the backup interface and added the static routes with a higher cost on each of the catalyst switches. but when vlan 204 is disconnected, one rsm will use the failover static routes while the other rsm still is using the first routes. I guess this is where the ip sla comes into play. I have IOS 12.2(26c) on each rsm, but the rsms do not have the ip sla option. I check the feature set for the ios and it should be there.

[ganeshh_iyer]

Jon's point is right how you make behave the switches in L2 or in L3 mode if L3 the best and easiet way is used to implement floating static route configuration which jon has pointed out in his post.

Configure two static routes one with higher Administrative distance so that it can act as backup when primary fails and if you want you can configure IP SLA to do everything automatic in case of primary link goes down and traffic will forwarded to secondary link.

check out the below link on ip sla hope that clear out your query !!

http://www.cisco.com/en/US/docs/ios/12_ ... sicmp.html


Ganesh.H

[broow]

thanks for the good advise and feedback.
I did add another vlan 205 to be the failover interface. Added the static routes, one for each vlan, example.

Code: Select all

ip route 172.25.0.0 255.255.0.0 172.28.1.1         for vlan 204
ip route 172.25.0.0 255.255.0.0 172.28.2.1  100    for vlan 205

all works until i disconnect the connection for vlan 204, one rsm will failover to the vlan 205 route, while the other keeps the vlan 204 route.

i tried to configure ip sla, but it is not an option. I am running 12.2(26c) and it shows it should have that feature, but no luck. I have to manually shutdown vlan 204 before it fails over. I guess this is what ip sla work correct.

[ganeshh_iyer]

Hi,

IP SLA will work if the track assoicted with SLA goes down then following action will done like earlier said if we track two interface by making destination ip ping with track associated with SLA configuration,so when the particular interface goes down then static route associated with SLA track will be cleared from routing table.


Ganesh.H

[sachinraja]

Hi Broow

You mean you have 2 different VLANs on both ends, and want to route between them, primary on the aerial fiber and backup on dark fiber ? and both these links are layer 3 right ? and connecting over fiber channel ?

since it is a general ethernet/fiber interface, the physical status of the interface might not go down if there is a fiber issue.. In case this is a direct fiber connection, you can use UDLD to detect uni-directional links, and fiber cuts.. incase the TX or RX has issues, UDLD can put the port on err-disabled state allowing the backup route to kick and routing to happen automatically... Once the fiber is restored, you can manually unshut the port to bring up the primary connection. though UDLD is layer 2 in nature, am sure it can be implemented on layer 3 links, if the channels are connected over fiber links.. check this URL:

http://www.cisco.com/univercd/cc/td/doc ... g/udld.htm

since your switch doesnt support IP SLA, you are left with less options.. does your ping to other end die if there is a fiber issue ? In that case you can use dynamic routing protocol like EIGRP between the switches and automatically advertise routes, based on the link status.. you can have higher cost to the backup link so that the routing makes it a failover link...


Hope this helps.. all the best..
Raj

[broow]

thanks for the feed back,

could you show me an example configuration please?

we have two 6500 hybrid systems, with vlan 204 between the two, on port 1/1 of each switch. I have the backup on 1/2 of each switch. does it need to be a different vlan of the same vlan. the fiber connection on 1/2 is billable when used, that is why it is inactived.

[sachinraja]

Hi

Do you still want VLAN 204 to span between the switches ? I assume that you have layer 3 point to point link between your switches.. in that case, you can create layer 3 interfaces on the switchport, for point to point connection...

udld aggressive

interface gig 1/1
description *** primary connection to switch 2****
no switchport
ip address x.x.x.x 255.255.255.252
udld port aggressive

interface gig 1/2
description **** backup port *****
no switchport
ip address y.y.y.y 255.255.255.252
delay 1200

** select appropriate delay values to make gig 1/2 as backup circuit for routing...

router eigrp 10
no auto-summary
network x.x.x.x (WAN network)
network 192.168.x.x (LAN networks)

and it really depends on how you want to route your standby routes.. try first with UDLD with static routes.. it might work since UDLD shuts the port down in case of fiber issues (TX or RX) and static route can disapper...


Hope this helps.. all the best
Raj

[broow]

would like to route between vlan 204
one other piece of information, our catalyst switch is hybrid, CAT IOS on the switch and Cisco IOS on the MSFC