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Home > Archive > CCIE > August 2001 > BGP question (1)
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| rootstock 2001-08-12, 3:58 am |
| a-b-c
a and b run ibgp in as1
c and b run ebgp in as2
every thing is ok, I can learn and ping between a and c
the question is the ip of a is 1.1.1.1, and I advertise 1.1.1.0 in bgp, c was not able to learn this route, I add mask net 1.1.1.0 mask 255.255.255.0, the c can not learn neither(ip classless had inputed), but if the I advertise 1.0.0.0 , then it work, why? | |
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| what is the ip address at router b and c ?? | |
| LANlord 2001-08-15, 12:37 pm |
| This may be a question for one of the moderators...they are pretty good. But I'll take a stab. Here goes:
As I understand this kind of situation, BGP will not advertise a route until it learns it from the IGP that is running. If there is no IGP running you can use the "no synchronization" command to disable that function. (You can still use the "no synchronization" command even with an IGP, but it is not generally advisable.) If you're using a classful IGP such as RIP, it does not recognize a classful subnet. For example, if your IP address starts with 10, that is a class A address with a default subnet mask of 255.0.0.0. Therefore RIP would not see anything past the 10 because it is classful. If you were using a classless IGP such as EIGRP that can understand VLSM, you probably wouldn't have this problem. Given the symptoms you're describing, that's my take on it. Godd luck! | |
| rootstock 2001-08-16, 7:36 am |
| yes, you are right, I understand now, thank you very very much. | |
| rootstock 2001-08-16, 7:59 am |
| one more thing
if I add command ip classless in the router,will 1.1.1.0 works? | |
| LANlord 2001-08-16, 8:20 am |
| I don't think the ip classless command applies in this situation. I think that is more for forwarding packets to a subnet that has no default route. | |
| rootstock 2001-08-16, 10:19 am |
| of course, default route or static route can solute this problem, but I don't want to use it. and I think it should work without manual route.
thanks for you answer  |
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