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?
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.
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