04-15-2010 07:02 AM - edited 03-04-2019 08:10 AM
guys suppose we are having 10 or 20 routes on WAN router learned from EIGRP
the wan routers has 10.15.15.0/24 to 10.15.X.0/24 etc (learned from EIGRP) and if we want to advertise a router in BGP can we use
10.15.0.0/16 route rather then putting 20 routes secondly do we have to put static null route for 10.15.0.0/16 or not
thanks for looking
04-15-2010 07:19 AM
You can advertise that /16, yes. You can also suppress the advertisement of the specific prefixes.
ip route 10.15.0.0 255.255.0.0 null0
router bgp 1
aggregate-address 10.15.0.0 255.255.0.0 summary-only
HTH
Victor
04-15-2010 07:27 AM
Thanks for the answer now i have a question do we really have to advertise the null0 route......if eigrp connection breaks
up even then the routes would be advertised in BGP ??? am i right or wrong secondly my main question remains stands
if we dont do null0 routes would this work or not??? thanks again
04-15-2010 07:40 AM
In order to advertise a route into BGP, the local router must have that route in its local routing table. The null0 route is not advertising, it's putting the /16 route into the local routing table so BGP can advertise it.
04-15-2010 07:50 AM
Is it possible for you to summarize the routes before your MPLS router? Then your MPLS router will already have the /16 route in its routing table and you don't have to worry about creating any to null0.
04-15-2010 08:05 AM
Hello Comsat,
the route to null0 is not strictly required you can use
network command for each component route
+ aggregate-address for the aggregate if you want to create the aggregate
usually the static to null0 is combined with a network command that matches directly the aggregate
Hope to help
Giuseppe
04-15-2010 09:02 AM
Thanks guys for your help now one more and final question.......actually there are two wan routers (the quetion is not abt the second one)
i am advertising three networks in BGP 10.4.1.0/24
10.5.1.0/24
10.6.1.0/24
the aggregation will be look like this (correct me if i am wrong)
aggregate-address 10.4.0.0 255.255.0.0 summary-only
aggregate-address 10.5.0.0 255.255.0.0 summary-only
aggregate-address 10.6.0.0 255.255.0.0 summary-only
is it correct ?
and if i want to prepend 10.6.1.0/24 (this the requirment)
so all i have to create a prefix-list and it should look like this
ip prefix-list prepend_network_to_isp seq 10 permit 10.6.0.0/16 (it shd be /16 not 24 right????)
route-map my_prepend permit 10
match ip address prefix-list prepend_network_to_isp
set as-path prepend X.X.X
now the imp question is shd i add permit staement in the route map (like same route _map for two other as i have read that then those two will be denied)
if yes how it shd look like
guys thanks again for looking
04-15-2010 09:16 AM
Hello Comsats,
at list one component router per aggregate-address has to be in the BGP table
the prefix-list should match the prefix you want to be prepended
ip prefix-list tobeprepended permit 10.6.0.0/16
you need a second empty route-map block or you will send out only one prefix
You should prepend only your own AS number one or more time.
Hope to help
Giuseppe
04-15-2010 09:17 AM
i am advertising three networks in BGP 10.4.1.0/24
10.5.1.0/24
10.6.1.0/24
the aggregation will be look like this (correct me if i am wrong)
aggregate-address 10.4.0.0 255.255.0.0 summary-only
aggregate-address 10.5.0.0 255.255.0.0 summary-only
aggregate-address 10.6.0.0 255.255.0.0 summary-only
As Giuseppe pointed out with the aggregate-address command you don't need a matching route in the routing table you just need at least one of the subnets of the aggregated address.
As for the above if you have 3 /24 networks why do you want to advertise them as 3 /16 summary addresses. I mean you can but is this really what you want to do eg.
10.4.0.0/16 as a summary address would be 10.4.1.0 -> 10.4.255.0, do you really want to do that ?
Jon
04-15-2010 09:48 AM
Jon you are right the main thing is which i cant get my head around is that i have around
70 networks 10.4.1.0 to 10.4.200.0/24 its mix actually now i am advertising in bgp
router bgp 1
neigbour X.X.X.C remote_as X route-map traffic_out out
network 10.4.1.0 mask 255.255.255.0 (its 24 not 16)
and then
aggregate-address 10.4.0.0 255.255.0.0 summary-only
!
ip prefix-list WAN_list seq 10 permit 10.4.0.0/16
route-map traffic_out permit 10
match ip address prefix-list WAN_list
This is the best i could think of
now my question is will it advertise all my 70 networks
Yes or no???
now shd i use null0 or not??? as i am getting all teh routes from IGP (all /24)
kindly guide me guys
04-15-2010 09:55 AM
comsats wrote:
Jon you are right the main thing is which i cant get my head around is that i have around
70 networks 10.4.1.0 to 10.4.200.0/24 its mix actually now i am advertising in bgp
router bgp 1
neigbour X.X.X.C remote_as X route-map traffic_out out
network 10.4.1.0 mask 255.255.255.0 (its 24 not 16)
and then
aggregate-address 10.4.0.0 255.255.0.0 summary-only
!
ip prefix-list WAN_list seq 10 permit 10.4.0.0/16
route-map traffic_out permit 10
match ip address prefix-list WAN_list
This is the best i could think of
now my question is will it advertise all my 70 networks
Yes or no???
now shd i use null0 or not??? as i am getting all teh routes from IGP (all /24)
kindly guide me guys
It won't advertise all 70 routes, it will advertise a summary route of 10.4.0.0/16 to EBGP peers.
Also because you are using the summary-only keyword i'm not sure what the route-map is meant to achieve because all the more specific 10.4.x.0/24 networks will not be advertised anyway.
You do not need to use Null0.
Jon
04-15-2010 10:17 AM
JON
so if /16 would be summarized still ppl can reach 70 networks that what i meant to ask......as i cant add 70 network commands in BGP
what is the solution am i doing wrong or what???
task is 70 routes with 10.4.X.X /24
so i have add 10.4.1.0/24 (which is the first subnet) and then aggregating them with /16
the route-map is cuz i am using 10.4.1.0/24 in network statement under BGP so i thought to use 10.4.0.0/16 in route-map tied up with prefix-list
look i am here as i m having problem and i m unsure
what do u think
and thanks again
04-15-2010 10:22 AM
comsats wrote:
JON
so if /16 would be summarized still ppl can reach 70 networks that what i meant to ask......as i cant add 70 network commands in BGP
what is the solution am i doing wrong or what???
task is 70 routes with 10.4.X.X /24
so i have add 10.4.1.0/24 (which is the first subnet) and then aggregating them with /16
the route-map is cuz i am using 10.4.1.0/24 in network statement under BGP so i thought to use 10.4.0.0/16 in route-map tied up with prefix-list
look i am here as i m having problem and i m unsure
what do u think
and thanks again
The "summary-only" keyword you are using with your aggregate address stops any individual subnets that makes up the summary address being advertised so only 10.4.0.0/16 will be advertised.
Yes, people should be able to reach all 70 networks because the summary address covers all those 70 networks but be aware it also covers a lot more than just 70 /24 networks.
Jon
04-15-2010 10:27 AM
Thanks JON 100 out of 100 (you deserve that) :-)
so am i doing the right thing putting 10.4.1.0/24 under BGP and doing aggregation with /16
r u happy with route-map???? does it make sence now???
04-15-2010 10:28 AM
comsats wrote:
Thanks JON 100 out of 100 (you deserve that) :-)
so am i doing the right thing putting 10.4.1.0/24 under BGP and doing aggregation with /16
r u happy with route-map???? does it make sence now???
I still don't think you need the route-map because your router will only advertise out the /16 summary address. However it's not doing any harm.
Jon
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