HSRP question

[wgranada1]

Quick question....can you set up HSRP on a WAN interface, one frame relay and the other ISDN line or is this for only ethernet?

[Jan Hrnko]

Hi Kuldeep,

What i understand through this Discussion, i just want 
to tell you plz correct me if i am wrong:
1. HSRP/VRRP/GLBP => It is used for LAN side redundancy
    ( as you shown with green colour in diagram)

Exactly! Very good!

2. IP SLA / PBR / Floating static route=> It is used for
    WAN side redundancy ( shown as blue and orange colour).

Yes, kind of. But to answer this completely, we would have to start a new thread . So I will pick up just some of the basic things.

IP SLA - This is an monitoring tool. Cisco IOS IP SLAs can be used to verify whether a network element (e.g., IP address or an open TCP port), is active and responsive. So it monitors IP address for example and can take some action if it is unavaible : for example, remove statically defined route to this destination from routing table ecc.

IP SLA is handy in a situation when your routes are dependent on some devices that is outside your network and you have no control of it, no routing protocols are defined between you and this device. This can be for example some devices inside your ISP network that you have no control of.

PBR - This feature can provide many benefits. One of the most obvious is load-sharing or load-balancing. It can also route packets based on their source address.

Float static route - This one can be used for redundancy as you said - configuring them as an backup alternative to some current routes.

Hope that helps a little.

Best regards,

Jan

[Kuldeep singh]

Hi jan,

Again i am coming to the old topic

I read this below url article and get confused bocz HSRP takes care

of only LAN side redundancy. then why we need to track WAN side

interface using this command:

hsrp-router1(config-if)# standby 1 track se0/0

http://www.itsyourip.com/cisco/how-to-configure-hsrp-in-cisco-ios-routers/

[Richard Burts]

KS

HSRP can not run on serial WAN interfaces. But HSRP may want to react to changes in the WAN interface even though it is not actually running on the WAN interface. Let me suggest a simple example to show what this means.

Assume that you have a LAN. And on that LAN are two routers (routerA and routerB). You want to run HSRP on the LAN interface of routerA and of routerB to provide redundancy for users connected on the LAN. Also assume that routerA has one WAN interface that is faster than the one WAN interface of routerB. So you may want to set the priority of HSRP in routerA so that it is the active router in HSRP. In this case user traffic from the LAN will use routerA as the next hop and will access the outside using the faster interface.

But what would happen if the WAN interface of routerA goes down? If routerA is still the active router in HSRP then user traffic will use routerA as the next hop. And it would work this way but it would not be efficient because traffic from the user would go to routerA which would forward it to routerB which would forward it to outside. It would be nice if routerA would give up being active if its WAN interface goes down so that routerB could become active and traffic will take the more efficient path.

That is what track does for HSRP. If HSRP on routerA tracks its WAN interface and if the WAN interface goes down then routerA lowers its HSRP priority and allows routerB to become active.

HTH

Rick

[ciscoamit_497]

Kuldeep,

In both cases, you can use the HSRP, But there are few exceptions..like for fig A--

You both upper routers are connected with a ethernet port with downstream router then you can configure the HSRP otherwise not...but this kind of design is not good for HSRP configuration.

Fig B

In this situation you can use both L2 or L3 switch to configure the HSRP or GLBP, watever u want.

But you have so many SVIs on L3 switch then you should enable the IP routing on MLS switch and configure a default static route that should be point towards the Virtual IP.

Then you will no need to configure any Dynamic routing protocol for the same...

Regards,

Amit

Hope this would be helpful to u....

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[Peter Paluch]

Hello Amit,

You both upper routers are connected with a ethernet port with downstream router then you can configure the HSRP

Actually, this would not work. The prerequisite for HSRP (and the other protocols as well) is that both routers running HSRP can hear each other directly so that they can backup themselves in a single network. This requirement is not met in Figure A - the routers 1 and 2 are split by router 3 and do not see/hear each other. They are in different IP networks. As HSRP/VRRP/GLBP always runs inside a single IP network, not above or across IP networks, the situation in Figure A is totally unsuitable for any of these protocols.

Best regards,

Peter

[ciscoamit_497]

Hi Warren,

You can't configure HSRP on any WAN interfaces. But you can track it using track config.

Regards,

Amit

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