Multiple routers on 1 subnet

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Aug 7th, 2007
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Do network administrators deploy this topology?

I read plenty of examples of technologies and how they benefit from mulitple routers on one subnet(multicast).

Who has the money to deploy 2+ routers per subnet?

To me this seems like a luxury most network designers have to go without.

Obviously having HSRP for router failover is nice, but this seems impractical to have router redundancy on the edge of every network.

I'm just looking for people with "real world" experience deploying multiple routers per subnet and using something like multicast.

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graemeporter Wed, 08/08/2007 - 00:27
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Hi there,

I'm not particularly experienced with HSRP, but the company I work for has a setup that provides HSRP across multiple subnets through a pair of redundant 6509 systems.

We have a number of buildings in an industrial estate that are connected to our central building by dark fibre. It's a switched network, with the switches in the remote sites having two connections (one to each 6509).

The 6509s are connected over two gigabit fibres. Each 6509 has two supervisor cards, each with an MSFC routing engine on it, so they provide inter-VLAN routing for each VLAN (each building has at least one data VLAN and one voice VLAN).

The 6509s are configured with HSRP so that each MSFC has an address on each VLAN, plus each VLAN has an HSRP group address. We give that address out as the default gateway address for each subnet.

So basically, each subnet has four routers, comprised of two dual-redundant layer 3 switches. We've had fibres and GBICs fail over the years, and during these outages, site connectivity has rarely been lost.

Does this help?

Kind regards,


jwdoherty Wed, 08/08/2007 - 07:22
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Yes, some companies do have, and spend, the money for multiple routers per subnet(, multiple network paths, and/or extra network equipment). Realize that with today's dependency on networks, having a single point of failure that can cause many users (sometimes thousands) to be "down" is often an unacceptable business cost that can be much greater than the cost of the additional equipment.

garybeach Wed, 08/08/2007 - 07:29
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We look after the network for a company that has many remote sites ranging from 2 or 3 users per site to 100-200 on some sites.

Obviously on the very small sites there is no IT skills available, but they are still very important to keep network connectivity up 24x7 so having a leased line router and a separate backup isdn router on each site is imperative to acheive this.

Using HSRP is very effective for company's this network.


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