04-12-2008 11:50 PM - edited 03-03-2019 09:32 PM
guys just a quick one why we turn on or off summarization in BGP???? can someone please give an exmple.....what r the factors which push to turn off or turn on the sum.....by default its on if i am not wrong.....secondly do we have to use static routes always in BGP???? in which scenario we use static routes and in which we dont...thanks a million in advance
04-13-2008 12:52 AM
Do you mean BGP Route Summarization ( the aggregate-address command as ex) or synchronization or auto-summary ?
The below URL have a good Contents for BGP tools.
http://www.cisco.com/en/US/docs/internetworking/case/studies/icsbgp4.html#wp19382
04-13-2008 01:43 AM
Summarization with network command
1. When Auto Summary is enabled
When auto-summary is enabled, it summarizes the locally originated BGP networks (network x.x.x.x) to their classfull boundaries (auto-summary is enabled by default in BGP) then
1. Any Subnet (component route, specific route) of that classfull network in the local routing table
2. Or the classfull network in routing table
prompts BGP to install the classfull network into the BGP table
So you need at least specific route in the routing table to force router to install the classfull network in BGP table and advertises it to BGP neighbors.
Ex. When you announce the network 172.16.0.0 via network command
router bgp 1
network 172.16.0.0 mask 255.255.0.0
auto-summary
The router will not install this route in BGP Table until it find the exact route Or at least specific route like 172.16.10.0/24 in routing table
2. When Auto Summary is disabled
To install any route in BGP table the
router must has an exact match for this
route in the routing table.
Ex. When you announce the network 172.16.0.0 via network command
router bgp 1
network 172.16.0.0 mask 255.255.0.0
no auto-summary
the router will not install this route in BGP Table until it has the exact route in routing table
to solve this issue we can add static route pointing to null 0
ip route 172.16.0.0 255.255.0.0 null 0
04-13-2008 01:49 AM
One Comment, Auto-summary not enabled by default.
Auto-summary behavior has changed across Cisco IOS releases. Initially, auto-summary was enabled by default. However, with Cisco bug ID CSCdu81680, this behavior has changed. In the latest Cisco IOS, auto-summary is disabled by default.
Check This.
Router(config-router)#do sh ver | inc imag
System image file is "sup-slot0:/c7200-p-mz.122-25.S14.bin"
Router(config)#router bgp 1
Router(config-router)#do sh run | be router bg
router bgp 1
no synchronization
bgp log-neighbor-changes
no auto-summary
04-13-2008 02:49 AM
Dear Mounir,
Auto-summary behavior has changed across Cisco IOS releases. Initially, auto-summary was enabled by default. In the latest Cisco IOS, auto-summary is disabled by default.
Thanks
04-13-2008 02:57 AM
What is the benefits of repeating the same words Mentioned above?
You said it's enabled by default and i'm clarifying that it's disabled by default in New IOS version, so it's was small correction.
Check the Bug-ID above if you don't believe that, or even try to lab it up.
04-13-2008 10:20 AM
Mounir
At first I thought that it was an unusual post. But then I noticed that it is not just a repetition of what you said. He repeated your correction and then he says "thanks". I take that as an acknowledgement that he understands and accepts your correction.
HTH
Rick
04-13-2008 03:12 PM
I thought that also, so i confirm the Bug-ID and the above example to make it clear, but no problem at all.
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