What is the benefit of Equal cost multipath routing ?

What is the benefit of Equal cost multipath routing ?

Post by Frank Wibison » Fri, 25 Oct 2002 14:42:35



Hi All,

Doing research on outgoing internet fail-over with two ADSL connection. I
made a script that essentially deletes the default routing and put in a
different one when one of the ADSL connection drops out. It seems to be
working fine.

My question is, people seems to be doing this system using ECMP which you
have to recompile the kernel and get the kernel to do change the default
route when the ADSL drops out. What is the benefit of doing it with ECMP ?

Cheers
Frank

 
 
 

What is the benefit of Equal cost multipath routing ?

Post by Birger Toedtman » Fri, 25 Oct 2002 20:08:42



> Hi All,

> Doing research on outgoing internet fail-over with two ADSL connection. I
> made a script that essentially deletes the default routing and put in a
> different one when one of the ADSL connection drops out. It seems to be
> working fine.

> My question is, people seems to be doing this system using ECMP which you
> have to recompile the kernel and get the kernel to do change the default
> route when the ADSL drops out. What is the benefit of doing it with ECMP ?

What you described above is overlay routing for *fail-over* cases.  This
means one link will be idle (maybe even down) all the time as long as the
other one is up and running.  The fail-over link will only be utilized when
the "normal" link goes down.

Peopla employ ECMP to use both links for traffic *simultaneously*, thus
providing load-balancing and fail-over at the same time.  This behaviour
is of course only desirable when the second link does not put additional
cost into the case.

Regards,

Birger

 
 
 

1. Looking for docs about equal cost multipath routing

Hi !

I am looking for a more in-depth decoumentation on

Equal Cost MultiPath routing,

because in the new advanced routing documentation this chapter is still
marked as todo (at least in the version I have read) and the ip command cref
was a bit too short.

There are several articles on the net which describe how to set up
applications of ECMP routing similar to bonding. Thats what Im looking
for, and it seems quite easy. But when I follow the instructions in these
articles, it doesnt work.  For example, if  I try to configure 2 equal cost
routes using the command

ip route add default nexthop via 1.0.0.x dev eth0 nexthop via
2.0.0.y dev eth1

it marks one of the two devices as DEAD immediately. And the funny thing
about it is, that the device which gets down seems to be randomly selected.

Perhaps I need some other software too (e.g a routing daemon) ? I dont
know. Compiling only a new kernel with most/all of the advanced routing
features enabled was of no use ...

But ANYdocumentations/HowTos/manpages you can give me would be a great help.

Thanks,
Sebastian

--

-=> Sebastian Bleikamp

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