Very Computer

by **Christopher P. Cericol** » Thu, 05 Apr 2001 01:09:16

In my office, we have two sets of bandwidth coming in. A fractional T1 and
a Cable Modem. Recently, we've been having the issues with the T and would
prefer to have our Linux router take both sets of bandwidth and fail-over to
the cable-modem if necessary. Short of making a script that is consistently
pinging and on 5-failures it changes the routing tables(which I'm not very
pleased with as a method), is there a package that use BGP to determine if
the route is up or down? All I need it to do is see, "Eth0 is dead, send
everything through Eth1". Thanks in advance.

--
Christopher Cericola

by **Dean Thompso** » Thu, 05 Apr 2001 08:55:09

Hi Chris,

Quote:> In my office, we have two sets of bandwidth coming in. A fractional T1 and
> a Cable Modem. Recently, we've been having the issues with the T and would
> prefer to have our Linux router take both sets of bandwidth and fail-over
> to the cable-modem if necessary. Short of making a script that is
> consistently pinging and on 5-failures it changes the routing tables(which
> I'm not very pleased with as a method), is there a package that use BGP to
> determine if the route is up or down? All I need it to do is see, "Eth0 is
> dead, send everything through Eth1". Thanks in advance.

Well there is a good news and there is bad news on this front. The BGP
protocol that you mention is capable of doing this but it isn't something that
you can just plonk on the Linux box and hope to work. The BGP protocol
requires support from both your ISP providers (I am pretty sure that you will
find that your providers wouldn't route BGP packets for you unless they are
really big companies). Additionally, you would also need to apply for a AS
number (Autonomous System Number) which effectively is your routing packet
number. Once you have all of that settled you would then need to have your
own netblock numbers as well.

As you can see BGP gets pretty complicated very fast and requires a lot of
support from external agencies like the group in your area which hands out
netblocks (these aren't that easy to get these days) as well as getting your
AS number and finding ISP's that provide support for you. Additionally, this
is very expensive and normally implemented at a higher level in CISCO border
gateways.

I am afraid the only way that you might be able to go is to write your script
which does the following:

* ping your eth0 remote gateway
* upon a failure you need to:
* Down the eth0 interface or suspend traffic going through it
* Bring up the eth1 interface
* Modify the routing table
* Restart any/all of your services which might be bound to a specific
interface
* Keep checking for the eth0 route to come good again. Once it goes good
do all the changes.

It gets tricky to do!

See ya

Dean Thompson

by **Clifford Kit** » Thu, 05 Apr 2001 23:24:39

Quote:> In my office, we have two sets of bandwidth coming in. A fractional
> T1 and a Cable Modem. Recently, we've been having the issues with
> the T and would prefer to have our Linux router take both sets of
> bandwidth and fail-over to the cable-modem if necessary. Short of
> making a script that is consistently pinging and on 5-failures
> it changes the routing tables(which I'm not very pleased with as
> a method), is there a package that use BGP to determine if the
> route is up or down? All I need it to do is see, "Eth0 is dead,
> send everything through Eth1". Thanks in advance.

Do you currently use BGP or is the Cable TA connection just a backup
and not doing anything? If it's just a backup then create a Cable
default route and then create a default route to the fractional
T1 connection.

Since the last default route created is the active one, traffic will
go through the fractional T1, but if the T1 fails and the routing
for it goes down as a consequence then the Cable default route will
automatically become the active one. When the T1 comes back up and
the default route is reset then it will be the active one again.

--

/* A salute to Inspector Baynes, of the Surry Constabulary, the only
police Inspector to ever best Mr. Sherlock Holmes at his own game.
"The Adventure of Wisteria Lodge", by Sir Arthur Conan Doyle. */

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