From: Jay Hennigan (jay@west.net)
Date: Thu Dec 19 2002 - 18:38:22 GMT-3
On Thu, 19 Dec 2002 JuniJinn@aol.com wrote:
> Senerio 1 ---> On an ASBR you use the "Default-Information originate"
> command and have a static default defined. My understanding of this command
> is that OSPF will pick the default up and propagate it.
Correct. Note that if the router does not have a default route (either
static or learned), it will not propagate one.
> Senerio 2 -----> On an ASBR you use the "default-information originate
> always" command and OSPF will inject a default route into its domain .
Correct, whether or not the ASBR actually has a default route.
> Senerio 3----> you Create a static default and redistribute the static into
> OSPF.
> Question...in senerio 2 what interface does OSPF choose as its next hop
> interface on the router that you put the command on ie the ASBR
It uses its IP routing table. If it doesn't have a next-hop for the
destination address, it will drop the packet.
> Question......Are all these senerios basicaly doing the same thing and if
> there is a difference..what is it?
Scenario 1: If the ASBR has a default route in its table, it will
propagate it via OSPF.
Scenario 2: The ASBR will propagate a default route via OSPF whether
or not it has one in its routing table. Packets forwarded to the ASBR
for destinations not reachable by the ASBR will be dropped.
Scenario 3: The ASBR will propagate the static default, provided that
it is in its routing table (the next-hop interface is up). If the next-hop
defined in the static is unreachable, the route is withdrawn. Scenarios
1 and 3 are similar, but metrics are going to be different depending on
how the default is specified/learned.
-- Jay Hennigan - CCIE #7880 - Network Administration - jay@west.net NetLojix Communications, Inc. - http://www.netlojix.com/ WestNet: Connecting you to the planet. 805 884-6323 .
This archive was generated by hypermail 2.1.4 : Fri Jan 17 2003 - 17:21:49 GMT-3