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First Hop Redundancy and PPPoE ?

So here's the thing...

We currently have a single EFM link that requires PPPoE authentication, which is handled by a 2901 ISR sitting behind the NTU device.

The server room is currently undergoing some major re-org and construction, with racks and components being moved about, unplugged, etc etc, on a daily basis, causing major disruptions to the network and users.

We have a spare 2901 laying about, and my first blush thoughts were to implement one of HSRP, VRRP or even GLBP... so that if (actually, WHEN) some bozo unplugs the router or its power source, the redundant router can step in and save the day, and I don't have all the lines on my phone light up.

But... then comes the issue of the PPPoE link, and how that fits into to picture, and I can't seem to figure it out.

Can one (all?) of these options support such a scenario? Is it possible at all ?

1 ACCEPTED SOLUTION

Accepted Solutions

Sorry for the delay,

Sorry for the delay, @mbundy999... apparently my notifications aren't getting through properly.

If you're only looking to track router status rather than link status, this shouldn't be too hard. HSRP or VRRP will do the trick. GLBP doesn't really make sense here because you will never have both links active at the same time, so load-balancing won't happen anyway.

On the primary router, you can configure your PPPoE dialler with a persistent connection. On the backup router, configure the PPPoE dialler for dial-on-demand with a fairly aggressive timeout for activity.

You can then configure your HSRP/VRRP between the two routers. The primary should be at the highest priority and configured for pre-emption. The backup should be configured for lower priority. Pre-emption is unimportant on the backup because it will never have a higher priority than the primary.

Because it has a persistent connection, the dialler interface on the primary router will stay up and handle traffic on the EFM connection. The backup router, even though it has a dialler interface, will not engage the PPPoE session unless it becomes the default router and starts receiving interesting traffic. When it does, it will engage the PPPoE session and (as long as the ISP realizes that the primary's session is down) will take over the link.

When the primary router comes back on-line, it will take over the HSRP/VRRP virtual IP and will start routing traffic over its own dialler interface. The interface may not come up right away if the backup router is still using it, but the aggressive activity timeout will cause the PPPoE session to drop fairly quickly and will allow the primary to establish once this occurs.

6 REPLIES

There are a few options here.

There are a few options here. Is the PPPoE connection using a reserved IP address on the link or is it dynamic?
New Member

Hi,I currently negotiate the

Hi,

I currently negotiate the address in the dialer, and pick up a few things using ipcp... just because it's safe to to it that way.

However, the EFM link uses a dedicated /30 subnet to provide static CE and PE addresses, so I probably could specify the known CE address on the outside interface(s), if push came to shove.

Sorry for the delay,

Sorry for the delay, @mbundy999... apparently my notifications aren't getting through properly.

If you're only looking to track router status rather than link status, this shouldn't be too hard. HSRP or VRRP will do the trick. GLBP doesn't really make sense here because you will never have both links active at the same time, so load-balancing won't happen anyway.

On the primary router, you can configure your PPPoE dialler with a persistent connection. On the backup router, configure the PPPoE dialler for dial-on-demand with a fairly aggressive timeout for activity.

You can then configure your HSRP/VRRP between the two routers. The primary should be at the highest priority and configured for pre-emption. The backup should be configured for lower priority. Pre-emption is unimportant on the backup because it will never have a higher priority than the primary.

Because it has a persistent connection, the dialler interface on the primary router will stay up and handle traffic on the EFM connection. The backup router, even though it has a dialler interface, will not engage the PPPoE session unless it becomes the default router and starts receiving interesting traffic. When it does, it will engage the PPPoE session and (as long as the ISP realizes that the primary's session is down) will take over the link.

When the primary router comes back on-line, it will take over the HSRP/VRRP virtual IP and will start routing traffic over its own dialler interface. The interface may not come up right away if the backup router is still using it, but the aggressive activity timeout will cause the PPPoE session to drop fairly quickly and will allow the primary to establish once this occurs.

New Member

Thanks for the assistance - I

Thanks for the assistance - I'll go dig out the spare 2901 and try to implement this.

 

Hello.Surely you may use HSRP

Hello.

Surely you may use HSRP or any other FHRP on LAN, but for WAN I would suggest to avoid using PPPoE and use just a pure Ethernet with /29 subnet.

In this case you will be able to run HSRP on WAN interface as well.

New Member

Unfortunately, avoiding PPPoE

Unfortunately, avoiding PPPoE is not an option.

"We currently have a single EFM link that requires PPPoE authentication"

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