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HSRP question

wgranada1
Level 1
Level 1

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?

2 Accepted Solutions

Accepted Solutions

Richard Burts
Hall of Fame
Hall of Fame

Warren

HSRP works on LAN/Ethernet interfaces. It does not work on Frame Relay or ISDN interfaces.

HTH

Rick

HTH

Rick

View solution in original post

Hi Kuldeep,

just to make things clear for you. This is scenario where you would use HSRP/VRRP/GLBP. The idea behind these protocols is the same but the way in which they function is slightly different. But don't become confused by that!

Look at this scenario. There are 2 routers on the same network and they are interconnected through switch. Hosts (PCs, Laptops) are connected through switch as well. To access the Internet, they have to have some default gateway ( i.e. Router). But which router they should use? There are two of them!

If you manually configure hosts to use only Router 1, Router 2 will be unused. And what if Router 1 fails? Router 2 could be backup because he also knows how to get to the internet, but how? Well, this is the time when HSRP/VRRP/GLBP (FHRP protocols) comes to play.

One more thing. The family of these protocols is called FHRP (First hop redundancy protocol)  and that should be enough to understand their purpose. They simply  provide redundancy of first hop from the view of host - therefore they  provide redundancy of default gateway.

When you configure these two Routers with any of these FHRP they will use ONE virtual IP address which you configure hosts to use and when one of the Router fails, the other will forward the traffic. In addition - you can configure it in such manner that Routers will keep an eye on the serial interface as well (track interface command) and when it comes down, the other Router will forward the traffic. This is handy because otherwise the FHRP would work only when the whole Router (or fa0/0) comes down. It would not detect any failure, hosts would send packet to this Router and Router, which serial interface is down, would drop the packets.

I hope that will make it more clear to you. So you only configure redundancy for hosts IN THE SAME NETWORK to the routers IN THE SAME NETWORK - 192.168.0.0/24 in my example. You CANNOT configure redundany like this between DIFFFERENT NETWORKS. The concept of FHRP is not designed to solve these kind of problems...

Best regards,

Jan

View solution in original post

35 Replies 35

Richard Burts
Hall of Fame
Hall of Fame

Warren

HSRP works on LAN/Ethernet interfaces. It does not work on Frame Relay or ISDN interfaces.

HTH

Rick

HTH

Rick

Thanks Rick for the info!!!

Warren

I am glad that my answer was helpful. Thank you for using the rating system to indicate that your question was resolved (and thanks for the rating). It helps make the forum more useful when people can read a question and can know that they will read a response which did resolve the question.

The forum is an excellent place to learn about Cisco networking. I encourage you to continue your participation in the forum.

HTH

Rick

HTH

Rick

Hi Richard,

Does HSRP works on Serial ports ??

No .it won't work on serail interfaces

The protocol is    designed for use over multi-access, multicast or broadcast capable
   LANs (e.g., Ethernet).

Link : http://tools.ietf.org/html/rfc2281

/Raju

Then what protocol i will use instead of HSRP where handoff is Serial ?

Hello,

Use a routing protocol instead of HSRP. If the handoff is a serial interface then it is supposed to be plugged into a router anyway, and the router should support routing protocols. HSRP is not to provide redundancy between routers - HSRP provides redundancy of the default gateway for PCs that don't speak routing protocols. If PCs spoke routing protocols, HSRP would not be necessary, and if you connect routers using serial interfaces, you don't need HSRP by definition.

Best regards,

Peter

Hi Peter,

1) You mean to say, HSRP not support on Serial Port. am i right ?

Second thing, Plz see given below diagram and queries related to it:

2) In Figure A, we can not configure HSRP as you stated in the post. am i right ?

3) In Figure B, what will happen in this scenerio, here can we configure HSRP or not ?

4) If figure B,

    if we are using L3 Switch(3560) then need to be configure HSRP

    if we are using L2 Switch(2960) then need to be configure GLBP

   am i right or wrong ?

Note:  i do not want to use any kind of Routing protocols

Hi Kuldeep,

1) You mean to say, HSRP not support on Serial Port. am i right ?

That is correct.

2) In Figure A, we can not configure HSRP as you stated in the post. am i right ?

Yes, that is correct. You can not use HSRP, VRRP or GLBP to provide redundancy for Router3.

3) In Figure B, what will happen in this scenerio, here can we configure HSRP or not ?

Assuming that the Cisco switch in the middle is operating as a Layer2 switch between routers 1 and 2, you can configure HSRP, VRRP or GLBP on both routers. However, this protocol is not going to provide redundancy for routers 1 and 2 but rather for client PCs connected to the switch. Remember: redundancy protocols like HSRP, VRRP or GLBP provide gateway redundancy for end hosts, not for routers on which they are running.

4) If figure B,

    if we are using L3 Switch(3560) then need to be configure HSRP

    if we are using L2 Switch(2960) then need to be configure GLBP

This is not correct. You are putting unrelated things together. If you want to run any gateway redundancy protocol, be it HSRP, GLBP or VRRP, the routers running this protocol must be in the same broadcast domain and hence in the same IP network. That it turn means that regardless of whether the switch is L3 or L2, it must be configured so that the routers can see themselves on the same network. If the switch is operating on L3 and actually divides the routers into two separate IP networks, then the routers do not see each other directly anymore and cannot backup themselves using any of these gateway redundancy protocols.

Best regards,

Peter

Hi Peter,

4) I am unable to understand the difference between HSRP and GLBP.

    I had read that HSRP works on L3 and GLBP works on L2,

    HSRP support multi gateway nut GLBP support single?

    Plz give simple example so that i can understand.

    http://www.ciscoconsole.com/lan-man/hsrp-vrrp-glbp/comparison-and-difference-between-hsrp-vrrp-and-glbp-protocols.html/

5) In Routing Protocols(RIP/OSPF/EIGRP),  can we configure these

    types of protocols without any restriction of Serial or ethernet port.

Hi Kuldeep,

4) I am unable to understand the difference between HSRP and GLBP.

    I had read that HSRP works on L3 and GLBP works on L2,

    HSRP support multi gateway nut GLBP support single?

    Plz give simple example so that i can understand.

I do not think that attributing HSRP or GLBP to L2 or L3 is a good approach. Basically, all three protocols - HSRP, VRRP and GLBP - operate on L3. Their main purpose is to make a group of routers in the same IP network appear as a single virtual router. Clients in this network use the IP address of this virtual router as their default gateway. Should the currently active router from this group fail, it will be transparently replaced by a different router while maintaining the same virtual IP address so that clients do not notice any change.

HSRP and VRRP are very similar. They both elect a single router from the group of routers that is the current owner of the virtual IP address and is the actual router that takes care of performing the default gateway functions. HSRP calls this router the Active router, VRRP calls it the Master. Other routers in the group monitor whether the Active/Master router still lives, and if not, they will elect a new Active/Mater router. However, the other routers are not being used as default gateways. That means that although you have multiple routers in your network, only one of them is actually doing all the data-forwarding work, and the others merely wait if they ever need to replace him. HSRP is a Cisco-proprietary protocol while VRRP is an open protocol but they both work quite similarly and produce very similar results.

The GLBP is a protocol that tries to utilize multiple routers in the same network at once. When deploying GLBP, up to 4 routers can be made forwarding, thereby splitting the load. This is the main difference between GLBP and the other two protocols: the GLBP utilizes multiple routers at once while HSRP and VRRP always make only a single router the active router. Let's not discuss the technical details how this is done - I believe at this point, the details are not necessary.

I see several technical inaccuracies in the article on ciscoconsole.com you have linked:

  • VRRP is not an IEEE standard - it is an IETF RFC.
  • All three protocols can be considered as working on OSI L3. In particular, GLBP is not an L2 protocol. On the contrary, the GLBP is built on top of HSRP (basically, it is a multi-instance HSRP with additional control plane). How can then GLBP be L2 if HSRP is L3?
  • The preemption for GLBP is incorrectly described although I do not want to discuss the gory details at this point.

5) In Routing Protocols(RIP/OSPF/EIGRP),  can we configure these

    types of protocols without any restriction of Serial or ethernet port.

Yes, that is correct. These protocols run over every interface capable of carrying IP packets. The protocols may behave slightly differently depending on whether they run over a point-to-point or multiaccess interface but the bottom line is that you can run routing protocols over every interface that can carry IP traffic.

Best regards,

Peter

Hi Peter,

This is my single location network diagram with router:

simple diagram.JPG

Now i want to configure HSRP for this Location with remote locations,

Plz describe this concept in two cases given below:

( explain through rough diagram)

1. Between two location (existing + other)

2. Between three location (existing + other two)

as per your statement, I need to remove Router from my location.

But after remove router, how i will access interent in LAN ?

Hello Kuldeep,

I do not understand what you are trying to achieve here. If I understand your topology correctly, each VLAN in which you could deploy the HSRP has only a single physical router - I assume it is the Cat3560. Without two or more routers in a single VLAN, you have no group of routers to deploy HSRP on. There is no physical redundancy in this network so you cannot configure a logical redundancy protocol...

as per your statement, I need to remove Router from my location.

This must be a misunderstanding - I do not recall making such a statement. I have probably indicated that if a particular network, i.e. a VLAN, is to be served by HSRP, it must be a single broadcast domain so no router must be splitting it into two.

Best regards,

Peter

Hi Peter,

This is my existing diagram and do not have any kind of HSRP

configuration.This diagram indicates only existing location

where i have one router, one cisco 3560 sw, eight cisco 2960 switch

only. Plz do not understand that it is diagram for two locations.

Now we are planning to connect two other location with this location.

I said before that you explain me according to yourself, you can take

your own example with rough diagram.

So how can i use HSRP ?

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