[c-nsp] Design Q

[Jessup, Toby]

Does the router really generates an ICMP redirect in this case? Or does
the router simply prefer the directly-attached eBGP path over its
neighbor's iBGP path (eBGP is better admin distance) and just forward
the packets without ICMP redirect?


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Bruce Pinsky
Sent: Wednesday, April 13, 2005 2:51 PM
To: info at beprojects.com; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Design Q


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Bruce Pinsky wrote:
| info at beprojects.com wrote:
| | I've got a design question that I am not sure about and was 
| | wondering if anybody has any insight.
| |
| | My intention is to have two separate Internet routers running eBGP 
| | to two separate upstreams and then iBGP to each other.  On the LAN 
| | side, they will each have their own IP, say .2 and .3 and share a 
| | HSRP address, say .1.  If I'm on the LAN, my DG is .1.  If I try to 
| | go to some random Internet address, I will go to .1 and we'll say 
| | that right now, that is router A.  If the address is best reached 
| | through it, it will forward the packet.  If it is best reached 
| | through B, which it learns via iBGP, it will send an ICMP redirect, 
| | assuming they are enabled, and tell me to go to .3 instead, which
will forward the packet.
| |   So on my pc, I will build a routing table as I move along.
| |
| | The question is, what do I do if I want to create 4-5 VLAN's.  Say I

| | have a layer3 switch like a 3750.  My initial thought would be to 
| | make it the DG for each vlan and it would have a default route of 
| | .1. However every time it gets a redirect, it will add it to it's 
| | routing table, right?  Now if one of the machines on one of the 
| | vlan's is a dns server or web server, theoretically, there could be 
| | thousands on different destinations, in which case the L3 switch 
| | will have thousands of routing entries and we all know that a lower 
| | end switch like the 3750 does not have enough memory to hold 100,000

| | routes.
| |
| | Am I better off setting up the links to the routers as trunks and 
| | using sub interfaces?  Or am I way off in my description above?  Or 
| | is there some other option?
| |
|
| Take a look at the Gateway Load Balancing Protocol (GLBP) whitepaper 
| at
|
http://www.cisco.com/en/US/partner/tech/tk869/tk769/technologies_white_p
aper0900aecd801790a3.shtml

|
|
| It describes several techniques and introduces the feature as well.
|

Oh and also take a look at HSRP with ICMP Redirects support at
http://www.cisco.com/en/US/customer/products/sw/iosswrel/ps1834/products
_feature_guide09186a00800e9763.html

- --
=========
bep

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