Network Engineering Asked by Jason Stangroome on December 7, 2021
Using example IPv4 addresses for discussion, assume I have used BGP to announce to the Internet the prefix 192.0.0.0/16 from datacenter A, and I have also announced a longer prefix 192.0.2.0/24 (a subset) from a different datacenter B.
In practice when datacenter B withdraws the longer /24 prefix, a period of service disruption (between 10 seconds to 2 minutes) has been observed where traffic to the /24 is effectively black-holed even though the datacenter A route continued to be announced.
The intent is that both datacenter A and B are capable of handling traffic for the same /24 but datacenter B is preferred when available.
Is this service disruption avoidable, or minimizable, and how?
Just as it takes time for the more specific announcement to propagate, it takes time for the withdrawal to propagate. But unlike for the former, the later results in traffic heading into a dead end as the route-removal traverses the tree.
In the chain of "A - B - C - D - E", where A is datacenter B, the instant B processes the withdrawal, it will stop routing traffic towards A, yet C, D, & E will still have the more specific path in their route tables. When C hands that traffic to B, B no longer wants it. Eventually the more specific will be withdrawn by B, and then likewise C will withdraw it, etc., etc. While this should, in theory, take a few seconds, the internet is a very big, very busy place.
Answered by Ricky on December 7, 2021
Get help from others!
Recent Questions
Recent Answers
© 2024 TransWikia.com. All rights reserved. Sites we Love: PCI Database, UKBizDB, Menu Kuliner, Sharing RPP