[c-nsp] ACL to block udp/0?

Hank Nussbacher hank at interall.co.il
Tue Dec 5 16:27:21 EST 2023

We encountered something strange.  We run IOS-XR 7.5.2 on ASR9K platform.

Had a user under udp/0 attack.  Tried to block it via standard ACL:

ipv4 access-list block-zero
  20 deny udp any any eq 0
  30 deny tcp any any eq 0
  40 permit ipv4 any any

Applied to interface:

  ipv4 access-group block-zero ingress
  ipv4 access-group block-zero egress

Yet, based on Kentik, we had no effect and the udp/0 attack just 
continued - as if the Cisco ACL is totally ignored.  Or am I missing 
something in the ACL listed above?



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