Which statements about BGP communities are true? (Select two.)

The correct answer is A. The community attribute is a transitive optional attribute. D. BGP communities are means of tagging routes to ensure a consistent filtering. (A) The BGP community attribute is defined as an optional transitive attribute (type code 8), meaning it is not required but must be forwarded to EBGP peers if present. (D) Communities are a flexible tagging mechanism used to group routes and apply consistent policy (filtering…

Advanced Addressing and Routing Solutions

Question

Options

AThe community attribute is a transitive optional attribute.
BHigh-order 16 bits encode the purpose and have local significance.
CLow-order 16 bits contain the AS number of the AS that defines the community meaning.
DBGP communities are means of tagging routes to ensure a consistent filtering.
EThe usable scope of communities is 1:0 through 65511:65555.

How the community answered

(46 responses)

A
91% (42)
B
4% (2)
C
2% (1)
E
2% (1)

Explanation

(A) The BGP community attribute is defined as an optional transitive attribute (type code 8), meaning it is not required but must be forwarded to EBGP peers if present. (D) Communities are a flexible tagging mechanism used to group routes and apply consistent policy (filtering, preference changes, etc.) across routers and ASes. (B) is incorrect - the high-order 16 bits hold the AS number, not purpose. (C) is reversed - the low-order 16 bits hold the locally defined value/purpose. (E) is incorrect - the reserved/well-known range starts at 0xFFFF0000; usable community values run from 1:0 through 65534:65535.

Topics

#BGP communities#transitive optional attribute#route tagging#BGP filtering

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