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BGP default routes

 
 
srp336@getcoactive.com
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      06-23-2005
I've got a router with 2 T1s going to different ISPs. Each ISP
advertises a default route to this router with the same weight via BGP.


What is the normal behavior in this situation? I was hoping to get the
router load sharing the outbound traffic equally between the 2 T1s.
What I get is all outbound traffic going out the T1 where the
destination IP address is the lowest. How can I equalize the outgoing
traffic?

 
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Barry Margolin
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      06-24-2005
In article <(E-Mail Removed). com>,
http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:

> I've got a router with 2 T1s going to different ISPs. Each ISP
> advertises a default route to this router with the same weight via BGP.
>
>
> What is the normal behavior in this situation? I was hoping to get the
> router load sharing the outbound traffic equally between the 2 T1s.
> What I get is all outbound traffic going out the T1 where the
> destination IP address is the lowest. How can I equalize the outgoing
> traffic?


Default routes are processed the same way any other routes are, by
comparing attributes like AS path length, weight, local preference, etc.
If all the BGP attributes are the same, the final tie-breaker is the age
of the route (older routes are preferred).

BGP is very poor at load balancing. Search the newsgroup archive for
"bgp load balance" to find past discussions and suggestions.

--
Barry Margolin, (E-Mail Removed)
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
 
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Igor Mamuzic
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      06-24-2005
Try with bgp multipath...
http://www.cisco.com/en/US/tech/tk36...80094431.shtml


B.R.
Igor


<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> I've got a router with 2 T1s going to different ISPs. Each ISP
> advertises a default route to this router with the same weight via BGP.
>
>
> What is the normal behavior in this situation? I was hoping to get the
> router load sharing the outbound traffic equally between the 2 T1s.
> What I get is all outbound traffic going out the T1 where the
> destination IP address is the lowest. How can I equalize the outgoing
> traffic?
>



 
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coolmaneesh@gmail.com
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      06-24-2005
I thought , it was the lowest "router-id". Is it the oldest route in
age ?

 
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srp336@getcoactive.com
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      06-24-2005
I've added 'maximum-paths 2' to my bgp stanza. I can't seem to tell any
difference. What's the point of bgp multipath?

I'm just trying to setup more equal utilization for our 2 T1s. Can BGP
not really get close to that? What's our alternatives?

 
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Vincent C Jones
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      06-25-2005
In article <(E-Mail Removed) .com>,
<(E-Mail Removed)> wrote:
>
>I'm just trying to setup more equal utilization for our 2 T1s. Can BGP
>not really get close to that? What's our alternatives?


Generally speaking, load balancing using BGP in a dual ISP setup is
considered "good" if you can get within a two-to-one ratio between
the two links, and that assumes significant numbers of internal
users and external destinations. Typically, a single user with a
single TCP connection to a single Internet server will see higher
performance if all the traffic goes over a single T1, and typical
load sharing set ups are configured to ensure that that is the case.

As Barry stated in his reply, Google Groups is your friend, as this
topic has been hashed to death multiple times over the past few
years, making old timers (the ones who actually know the answers)
reluctant to waste their time doing it yet again.

--
Vincent C Jones, Consultant Expert advice and a helping hand
Networking Unlimited, Inc. for those who want to manage and
Tenafly, NJ Phone: 201 568-7810 control their networking destiny
http://www.networkingunlimited.com
 
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Barry Margolin
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      06-25-2005
In article <(E-Mail Removed) .com>,
"(E-Mail Removed)" <(E-Mail Removed)> wrote:

> I thought , it was the lowest "router-id". Is it the oldest route in
> age ?


The tie-breaker used to be lowest router-id. Several years ago Cisco
changed it to age.

--
Barry Margolin, (E-Mail Removed)
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
 
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Barry Margolin
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      06-25-2005
In article <(E-Mail Removed) .com>,
(E-Mail Removed) wrote:

> I've added 'maximum-paths 2' to my bgp stanza. I can't seem to tell any
> difference. What's the point of bgp multipath?


I think maximum-paths will only insert multiple routes learned from the
same ASN. So the point of it is when you have multiple T1's to the same
ISP.

> I'm just trying to setup more equal utilization for our 2 T1s. Can BGP
> not really get close to that? What's our alternatives?


There are some tricks you can play with route-maps that set weights
based on as-path access lists. Like I said before, search the archives.

--
Barry Margolin, (E-Mail Removed)
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
 
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coolmaneesh@gmail.com
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      06-27-2005
Thanks Barry

 
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Igor Mamuzic
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      06-27-2005
I'm not quiet experienced in BGP, but If you can get two routes to the same
destination learned from BGP in your IP routing table, then try to play
around with cef load balancing. It requires two or more prefixes to the same
destination in it's FIB to do proper load balancing (CEF load balancing is
not, AFAIK, enabled by default).

B.R.
Igor

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> I've added 'maximum-paths 2' to my bgp stanza. I can't seem to tell any
> difference. What's the point of bgp multipath?
>
> I'm just trying to setup more equal utilization for our 2 T1s. Can BGP
> not really get close to that? What's our alternatives?
>



 
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