Wednesday, 15 September 2010

BSCI - Manipulating Routing Updates - Route-map permissions

When compiling a Route-map(RM), you set an access control list (ACL) then use the Route-map to match addresses set out in that ACL to apply your chosen criteria in the Set field of the Route-map.

Now the question is given the combination of permit or deny statements in the ACL and the permit or deny statement of the Route-map what is the out come for a packet.

The following is what happens to a given packet when the permit or deny statements are considered:

ACL = Permit
RM= Permit
Result = Packet Permitted to proceed via the route-map. That's to say the packet is permitted to be permitted.

ACL = Deny
RM = Permit
Result = Packet Denied. The packet is denied from being permitted.

ACL = Permit
RM = Deny
Result = Packet Denied. The packet is permitted to be denied.

ACL = Deny
RM = Deny
Result = Packet PERMITTED. The packet is denied from being denied. If it isn't allowed to be denied, it must, therefore, be permitted.

Bit of a weird one to get your head round but it's an obvious trick to chuck in there when you're under pressure so keep an eye out.

1 comment:

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