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ISDN backup using floating static routes

Unanswered Question
Jul 8th, 2002
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I am configuring an ISDN dialer backup, all works ok with the following static route


Ip route 0.0.0.0 0.0.0.0 172.16.40.5


But will not work with the following static route


Ip route 0.0.0.0 0.0.0.0 bri0


I get do a debug ip packet and get an encapsulation failed message, why will this not work with the second static route, is it possible to get this working so I can standardise all our remote office configs.



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Anonymous (not verified) Mon, 07/08/2002 - 09:55
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The issue concerns one of mapping layer

3 addresses to layer 2 (DDR), which is

a multipoint (ie can dial multiple sites)

interface. When you have


ip route 0.0.0.0 0.0.0.0 172.16.40.5


Every packet will be given a next hop

destination address of 172.16.40.5; if

this points to a DDR interface, and

that DDR interface has a dialer map for

the IP address 172.16.40.5 then all is

well.


However, if you have


ip route 0.0.0.0 0.0.0.0 bri 0


Then (let's say) we receive an IP

packet with a destination address of

10.1.1.1; the routing table points us

to BRI0, and unless BRI0 has a dialer

map for 10.1.1.1 we will get an encapsulation

error.


With DDR interfaces the preferred approach

is to use a specific next hop address; if

that is a problem, and you are only dialing

to one site, use dialer profiles (which

are point to point interfaces) and the

BRI static route should work.


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