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
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 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 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 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? -----Original Message----- From: Mike Leber [mailto:mleber@he.net] Sent: Saturday, September 14, 2002 4:48 PM To: Lupi, Guy Cc: 'nanog@merit.edu' 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: 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:mleber@he.net] Sent: Saturday, September 14, 2002 4:19 PM To: Lupi, Guy Cc: 'nanog@merit.edu' 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.
+----------------- H U R R I C A N E - E L E C T R I C -----------------+ | Mike Leber Direct Internet Connections Voice 510 580 4100 | | Hurricane Electric Web Hosting Colocation Fax 510 580 4151 | | mleber@he.net http://www.he.net | +-----------------------------------------------------------------------+
+----------------- H U R R I C A N E - E L E C T R I C -----------------+ | Mike Leber Direct Internet Connections Voice 510 580 4100 | | Hurricane Electric Web Hosting Colocation Fax 510 580 4151 | | mleber@he.net http://www.he.net | +-----------------------------------------------------------------------+
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:mleber@he.net] Sent: Saturday, September 14, 2002 4:48 PM To: Lupi, Guy Cc: 'nanog@merit.edu' 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:mleber@he.net] Sent: Saturday, September 14, 2002 4:19 PM To: Lupi, Guy Cc: 'nanog@merit.edu' 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
On Sat, 14 Sep 2002, 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
Why cant the customer point default at you? Makes more sense from an admin point of view
table. You're right, if I am the only gateway then it really doesn't
Why bother running BGP in that case! If you're the only transit but they have other peers they may as well default to you.
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
If they are clever about the 2 BGP feeds they can allow the 2 ISPs to send a full table but filter inbound prefixes that you know are not going to be installed eg if your transits are AS2 and AS3 then you can immedaitely filter all routes from AS2 with AS3 in the path and vice versa.. if these are large ISPs that will seriously reduce the routes received!
router that can accept 2 providers feeding it full tables (why you would 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 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?
I've not done this but presumably you could either use default-originate or if you want to guarantee some level of functionality in your network you could insert a default into BGP at some other core router and then allow this route out to this peer and not others, if your edge router loses connectivity with the core router originating the route then it will withdraw it.. (assumes no default in your routing table other than that of course) Either way, as I say tho I'd suggest the customer does the engineering and not you! Steve
-----Original Message----- From: Mike Leber [mailto:mleber@he.net] Sent: Saturday, September 14, 2002 4:48 PM To: Lupi, Guy Cc: 'nanog@merit.edu' 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:mleber@he.net] Sent: Saturday, September 14, 2002 4:19 PM To: Lupi, Guy Cc: 'nanog@merit.edu' 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.
+----------------- H U R R I C A N E - E L E C T R I C -----------------+ | Mike Leber Direct Internet Connections Voice 510 580 4100 | | Hurricane Electric Web Hosting Colocation Fax 510 580 4151 | | mleber@he.net http://www.he.net | +-----------------------------------------------------------------------+
+----------------- H U R R I C A N E - E L E C T R I C -----------------+ | Mike Leber Direct Internet Connections Voice 510 580 4100 | | Hurricane Electric Web Hosting Colocation Fax 510 580 4151 | | mleber@he.net http://www.he.net | +-----------------------------------------------------------------------+
participants (3)
-
Henry Yen -
Lupi, Guy -
Stephen J. Wilcox