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mikey250
 asked on

bgp ibgp/ebgp & as_path attribute - query

hi ive configured a small test network representing both 'ibgp & ebgp with router 1 connected to both router 2 & 3.

1st task:

note: router 1 & 2 have configured both 'bgp & ospf representing igp'

- router 1 is connected via a serial cable to router 3
- router 1 is also connected via a fastethernet cable to router 2
- router 1 also has a single loopback

- router 2 is connected to router 1
- router 2 also has a single loopback

- router 3 is also configured with just 'bgp & not ospf' as it is external
- router 3 has also a fastethernet connection to a lan

ive configured on router 1 & router 3 for example:

router 1

router bgp 200
network 172.16.1.0 mask 255.255.255.0

router 3

router bgp 100
network 192.168.1.32 mask 255.255.255.224

2nd task:

ive configured a small network for using the 'as_path attribute' - but instead of configuring something simular to above 'mask' command ive done the following:

router 1

router bgp 300
no synchronization
neighbor 192.168.1.5 remote-as 100
neighbor 172.16.1.18 remote-as 65000
network 202.2.2.0

router 2

router bgp 100
no synchronization
neighbor 192.168.1.6 remote-as 300
network 201.1.1.0

router 3

router bgp 65000
no synchronization
neighbor 172.24.1.17 remote-as 300
network 203.3.3.0

question.  i assume it is something to do with how ibgp & ebgp distinguish itself with 'bgp' as why step 2 does not use the 'mask' command ?
RoutersNetworking ProtocolsNetwork ArchitectureNetworkingNetwork Management

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mikey250

8/22/2022 - Mon
ASKER CERTIFIED SOLUTION
pergr

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mikey250

ASKER
hi pergr, apologies for taking so long to return back to this question.

i had previously configured the following for 'bgp'

- sanjose3 serial0 & 1 connected to isp1a & isp12

note: all 3 routers have separate 'as' numbers

- sanjose3 - loopbacks were set as 'network' statements:
network 192.168.0.0
network 192.168.1.0

- isp1a - loopback was set as 'network 12.0.1.0 mask 255.255.255.0

- isp2 - loopback was set as 'network 172.16.1.0 mask 255.255.255.0

"so when you say the below im not getting my head around it although i understand what you have said, unless it refers to not using loopbacks or something: uuuuum

The "mask" part of the network statement is need only when you want to use a none "classful" mask. For example:

network 192.168.1.32 mask 255.255.255.224

If you had not included the mask, the router would have assumed the mask was 255.255.255.0."
mikey250

ASKER
hi pergr, i have used a 'classful' address.!!!

question 1.

i responded on my last 'thread' about 'mask', but my query is ive used a 'classful mask', although you say 'mask' is supposed to be used as per below:

The "mask" part of the network statement is need only when you want to use a none "classful" mask. For example:

network 192.168.1.32 mask 255.255.255.224 - ?
SOLUTION
pergr

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mikey250

ASKER
hi,

oh ok so if 'no mask' command was added it would by default be taken as a classful mask .!!

so by myself using a 'classful address - 255.255.255.0 - ie adding this command statement are you saying it still reacts in the same manner & so it does need to be a 'classless address' to get the correct routing response ?
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pergr

Yes, for 192...., if you do not include a mask, it takes it as if you had entered a mask 255.255.255.0.
mikey250

ASKER
ok i will need to make a note of this!!
mikey250

ASKER
sound advice!!
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