bgp 1.0 Flashcards
Q
A
What is criterion 0 for the start of the best path selection for an NLRI?
The Next hop needs to be reachable
BGP Attributes
Weight, Local Pref, Locally originated, AS Path, Origin, MED, External over internal, Lowest IGP Cost, Tie Breakers
What is the tie break for external routes?
The oldest route wins
What is the tie break for internal routes?
The smallest BGP router ID wins
Is it possible for two BGP routers to have the same router ID?
True
If a prefix is originated from a router with the same router ID but from different cluster lists, which route should be chosen as the best? If the cluster list is the same?
Prefers the smallest cluster list, Prefers the smallest neighbor IP address
What are the points of application for BGP policies?
Global, Neighbor, Prefix
What is the weight value for locally injected and remotely injected routes?
Local 32768, Remote 0
Is it not possible to apply weight per neighbor?
False, it is possible
What is the default value of the local preference attribute?
100
Does LP also affect subASes?
True
How is the origin attribute evaluated?
i > e > ?, IGP better than EGP better than incomplete
What is the default MED value?
There is no default value, IOS considers 0 as the best metric
Is it possible to change the MED to consider a prefix without MED as having the worst possible metric instead of the best?
True
What is Cisco’s name for the community in the export subconfed?
local_as
AS Path validation specification which has become known as ______
BGPsec
_______ is implemented via an ___________ BGP path attribute called__________, that carries digital signatures produced by each autonomous system propagating the update message. The digital signatures provide confidence that every AS on the path of ASes listed in the update message has explicitly authorized the advertisement of the route.
BGPsec, optional non-transitive, BGPsec_Path
When two BGP routers negotiate the use of BGPsec between them, they replace the AS_PATH attribute in BGP updates with a new_________ attribute, which performs the same function—but now securely.
BGPsec_Path
When a BGPsec-capable router talks to a regular BGP router, it converts the BGPsec_Path to a regular______, stripping off all security information in the process.
AS_PATH
For BGPsec to work, there must be an unbroken path of BGPsec-capable routers between where a BGP update is originated and where it’s validated.
True
BGPsec is note resource-intensive.
False
BGP updates will be larger due to the inclusion of signatures and supporting information.
True
Processing updates will take same time as usual updates
False, processing updates will take more time as each AS hop in the AS path requires a signature check.
The BGP Weight is not a BGP attribute
True, it’s an administrative weight
Default weight is 0 for incoming updates and 65535 for redistributed routes
False, it is 0 and 32768
What are the ways to configure the weight?
Via route-map incoming updates / redistribution and by neighbor
What is the default LP?
100
The default local preference cannot be modified
False, via command bgp default local-preference
How should the prepend be done on IOS XR in the inbound direction?
route-policy SetAS, prepend as-path own-as 3, end-policy
How should the prepend be done on IOS XE in the inbound direction?
route-map SetAS, set as-path prepend last-as 3
The MED propagated via eBGP from AS1 to AS2 but this same MED does not propagate to AS3
True
The MED can only be propagated to external neighbors
False, both
The MED propagated from an IBGP peer will be passed to an eBGP peer
False, it will not
Which attribute does the default-metric command configure?
MED
