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Redistribution
routing protocol redistribution
25
Computer Networking
Professional
09/20/2016

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Term
what routes will be redistributed with the "redist eigrp" command?
Definition
learned eigrp internal routes and connected interfaces.
Term
what if you don't want to redsitribute connected routes?
Definition
exclude using route-map.
Term
redistribution behaviour of distance vector protocols?
Definition
routes must be used in the routing table if they are to be redistributed.
Term
redistribution behaviour of ospf?
Definition
routes can be redistributed if they are in the database and have routing bit set. This is not always the case, such as when there are duplicate RIDs in the network.
Term
redistribution behaviour of bgp?
Definition
can be redistributed if in the BGP table. Will show "RIB failure" if IGP is preferred over iBGP.
Term
what if multiple processes of the same protocol advertise the same route with the same metric?
Definition
lowest process ID will be chosen.
Term
what if different protocols have had their AD changed to the same value?
Definition
default values will be used.
Term
ODR AD?
Definition
160
Term
NHRP AD?
Definition
250
Term
default RIP seed metric?
Definition
doesn't have one. Set during redistribution or with "default-metric".
Term
default EIGRP seed metric?
Definition
connected/static will use interface metric.
Protocols will require:
1. define during redist.
2. default-metric.
3. route-map.
Term
default OSPF seed metric?
Definition
type-2, value 20.
Term
OSPF route preference?
Definition
intra > inter > E1 > N1 > E2 > N2
E1 & N1 vs E2 & N2 - forward metric is key for E2/N2.
Term
OSPF external to BGP?
Definition
denied by default, must be specified "redistribute ospf {pid} match internal external"
Term
OSPF classfull/classless considrations.
Definition
use the "subnets" keyword when redistributing with OSPF.
Term
ospf/eigrp loop prevention?
Definition
set router-id.
Term
loop/feedback prevention strategy?
Definition
1. protect higher AD routes from feedback.
2. ensure router always routes to source protocol.
3. prevent sub-optimal routing.
Term
preventing loops and feedback - methods.
Definition
Tagging
mutual redistribution
distance
filtering with distribute-lists etc.
Term
describe control plane loop.
Definition
unstable routing - route thrashing or count to infinity.
Partial reachability.
Term
describe data plane loop.
Definition
routing is settled, but wrong (looped) path is selected.
No reachability.
Term
tools to identify loops?
Definition
ping script.
Debug ip routing, problem router will give reason for routing changes.
Check age of routes.
Ip route profile.
Traceroute.
Term
ospf distribute-list banana skin?
Definition
black holes - only removes from routing table.
Term
ospf distance banana skin?
Definition
only locally significant, may lead to data plane loops.
Term
"ip route profile" config?
Definition
"ip route profile" - takes periodic snapshot of routing table and changes.
"sh ip route profile" - only top row should be populated.
Term
how does 2-way redistribution at multiple points help?
Definition
router will not listen to routes it is also redistributing.
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