06-03-2010 05:42 AM - edited 03-04-2019 08:39 AM
What is the Correct Answer
Scenario /Daigram attached
Conditions
1. synchronization is OFF
2. NO IGP is running in AS 65500
Which router in AS 65500 is going to end up advertising a route to network
172.16.0.0?
A. B only
B. E only
C. B and E only
D. B, C and D only
E. B, C, D, and E
Solved! Go to Solution.
06-03-2010 06:25 AM
Hello Sohail,
RB advertises the net to all iBGP neighbors
because sync is OFF RE is going to advertise to its eBGP neighbor RF (it wouldn't do it with sync on)
so answer C
Hope to help
Giuseppe
06-03-2010 07:18 AM
Hello Sohail,
>> and what about RB at that point will it also have to wait before adverstsing
RB learns the route from an eBGP neighbor that is directly connected and can advertise it to its iBGP neighbors actually RB should be the device that reditribute the route into IGP also.
The objective of synchronization is to avoid to have a routing black hole inside an AS so it is RE the device that can be affected by sync settings.
I may be wrong but it should be in this way
Hope to help
Giuseppe
06-03-2010 06:25 AM
Hello Sohail,
RB advertises the net to all iBGP neighbors
because sync is OFF RE is going to advertise to its eBGP neighbor RF (it wouldn't do it with sync on)
so answer C
Hope to help
Giuseppe
06-03-2010 06:58 AM
Hi Giuseppe
You mean IF SYNC is turned ON , then RE will advertise only if all IBGP have learned about the NET
and what about RB at that point will it also have to wait before adverstsing
Synchronization says
" When an AS provides transit service to other ASs and if there are non-BGP routers in the AS, transit
traffic might be dropped if the intermediate non-BGP routers have not learned routes for that traffic
via an IGP. The BGP synchronization rule states that if an AS provides transit service to another AS,
BGP should not advertise a route until all of the routers within the AS have learned about the route
via an IGP."
06-03-2010 07:18 AM
Hello Sohail,
>> and what about RB at that point will it also have to wait before adverstsing
RB learns the route from an eBGP neighbor that is directly connected and can advertise it to its iBGP neighbors actually RB should be the device that reditribute the route into IGP also.
The objective of synchronization is to avoid to have a routing black hole inside an AS so it is RE the device that can be affected by sync settings.
I may be wrong but it should be in this way
Hope to help
Giuseppe
06-03-2010 10:19 AM
Sohail,
With the current scenario, Assuming no router reflectors are configured, and without any type of filteration in router B, Then AS 65000 can Only recieve routes from (Router B). Router D Can also advertise Networks to Router B and then to AS 65000 IF and Only IF the networks are originated from Router D itself.
The Synchronization rule here is not applicable.
HTH
Mohamed
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