North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: BGP Default Route
On Sat, Sep 14, 2002 at 04:49:23AM -0400, Lupi, Guy wrote: > Assume I am originating default for customers that only want a default > route, or a default route and some portion of the full Internet routing > table. You're right, if I am the only gateway then it really doesn't If you're the only gateway, why would you be running eBGP with the customer at all (unless the customer has his/her own peers)? > matter. Obviously if there is more than one provider it would be better for > the customer to accept full routes, but there are some customers out there > that have 2 providers and don't want to assume the cost of purchasing a > router that can accept 2 providers feeding it full tables (why you would Perhaps the customer's upstreams are not in the same "tier" (e.g. one provider is expensive tier 1 and is metered, and the other provider is a local, cheap, but tier 2/3). If the smaller provider is not as well connected as the larger one, full routes can be sub-optimal, no? > assume the cost of 2 providers and not a reasonably priced router that can > handle it I don't know, but I have run into it before). I am really just There are customers who are multihomed at geographically distinct locations; packets routed to any BGP border from interior (non-BGP) routers are often better off just taking the nearest default 0/0 outbound. > curious as to how people implement this and their reasoning for selecting a > particluar method. Is your method the one you stated before, default > origination from the router that is directly connected to the customer? FWIW, the large tier-1's we've had experience with do just that, and assume that their POP's are "never" cut off from the rest of the 'net. > -----Original Message----- > From: Mike Leber [mailto:[email protected]] > Sent: Saturday, September 14, 2002 4:48 PM > To: Lupi, Guy > Cc: '[email protected]' > Subject: RE: BGP Default Route > > The answer is you can do it all sorts of ways. > > Why are you originating default? > > If you are originating default because you are the only gateway for a > customer, whatever partial connectivity your router has is better than > effectively turning them off if you have a network partition. > > If your customer has more than one upstream they really should take full > views so they have the ability to make routing decisions based on that > information. This fixes your concern and is the best engineering choice. > > A hack would be to conditionally announce default based on the presence of > some specific other route. This would be doing additional work to > implement a suboptimal solution which a simpler use of BGP (full views) > fixes automatically. > > Yes, as much as you can, your routers should be meshed with more than one > connection each. > > Mike. > > On Sat, 14 Sep 2002, Lupi, Guy wrote: > > > I see what you are saying, and I understand that the default route would > be > > originated per neighbor, or per peer group for all neighbors within that > > peer group. My biggest concern is that if the aggregation router with > this > > configuration was to lose connectivity back to the routers which provide > it > > with external routing information, it would still announce the default to > > that neighbor. Do you feel that this is an acceptable risk, taking into > > consideration that the aggregation router has redundant connectivity to > > those routers that provide it with it's external routing information and > it > > is highly unlikely that the router would lose it's view of the world? > > > > -----Original Message----- > > From: Mike Leber [mailto:[email protected]] > > Sent: Saturday, September 14, 2002 4:19 PM > > To: Lupi, Guy > > Cc: '[email protected]' > > Subject: Re: BGP Default Route > > > > On Sat, 14 Sep 2002, Lupi, Guy wrote: > > > I was wondering how people tend to generate default routes to customers > > > running bgp. > > > > Typically you would only originate default via BGP to a customer that > > isn't taking a full view. > > > > neighbor 10.10.10.2 default-originate > > neighbor 10.10.10.2 filter-list 9 out > > > > ip as-path access-list 9 deny ^.*$ > > > > > Is it from the aggregation router that customers are directly > > > connected to, or from one or more core/border routers? > > > > In the example above the default originate is done via a specific BGP > > session, so it isn't router wide on either core or border routers. > > > > > If one is using a default route to null 0... > > > > I'll leave the rest of this for somebody else to answer. > > > > Mike. -- Henry Yen Aegis Information Systems, Inc. Senior Systems Programmer Hicksville, New York
|