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108 Cards in this Set
- Front
- Back
BGP State: Idle
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The initial state of a BGP connection. In this state, the BGP speaker is waiting for a BGP start event, generally either the establishment of a TCP connection or the re-establishment of a previous connection. Once the connection is established, BGP moves to the next state. |
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BGP State: Connect |
In this state, BGP is waiting for the TCP connection to be formed. If the TCP connection completes, BGP will move to the OpenSent stage; if the connection cannot complete, BGP goes to Active |
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BGP State: Active |
The BGP speaker is attempting to initiate a TCP session with the BGP speaker it wants to peer with. If this can be done, the BGP state goes to OpenSent state. |
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BGP State: OpenSent |
The BGP speaker has sent an OPEN message and is waiting to receive an OPEN message from the remote BGP speaker |
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BGP State: OpenConfirm |
Once the BGP speaker receives the OPEN message and no error is detected, the BGP speaker sends a KEEPALIVE message to the remote BGP speaker |
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BGP State: Established |
All of the neighbor negotiations are complete. You will see a number which tells us the number of prefixes the router has received from a neighbor or peer group. |
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BGP Best Path Selection |
1. Weight (Higher is preferred) 2. Local preference (Higher is preferred) 3. Self originated (Locally injected is preferred over iBGP/eBGP learned) 4. AS-Path (Smaller is preferred) 5. Origin (Prefer ORIGIN code I over E, and E over ?) 6. MED (Smaller is preferred) 7. External (Prefer eBGP over iBGP) 8. IGP cost (Smaller is preferred) 9. EBGP Peering (Older is preferred) 10. RID (Lower is preferred) |
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Define: Well Known Mandatory (BGP Attributes) |
Recognized by all implementations of BGP and must appear in a BGP update message. If missing, a notification error will be generated. |
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Define: Well Known Discretionary (BGP Attributes) |
Recognized by all implementations of BGP but may not be sent in the BGP update message (include LOCAL_PREF, ATOMIC_AGGREGATOR). |
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Define: Optional Transitive (BGP Attributes)
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May or may not be recognized by all BGP implementations. Because the attribute is transitive, BGP accepts and advertises the attribute even if it is not recognized (include Community attribte). |
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Define: Optional Non-Transitive (BGP Attributes) |
May or may not be recognized by all BGP implementations. Whether or not the receiving BGP router recognizes the attribute, it is nontransitive and is not passed along to other BGP peers (include MED). |
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Originator |
Attribute created by a route reflector. This is the RID of the router that originated the prefix |
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Use this command to have the system calculate a second BGP best path |
(address-family config mode) bgp additional-paths select {best-external [backup]|backup} |
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Define UPDATE message |
A BGP speaker receives routes and their attributes through an update message |
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Command used to redistribute iBGP into an IGP |
bgp redistribute-internal |
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Command to ensure the comparison of the MED variable when choosing routes advertised by different peers in the same AS |
bgp deterministric-med |
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Change the default AD (two commands) |
distance bgp |external-distance| |internal-distance| |local-distance| distance -distance- {ip address {wildcard}} [ip-standard-list|ip-extended-list} |
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When aggregating routes, if the AS_SEQ of the component routes differ in any way, the new summary subnet will |
have its AS_SEQ set to null, unless the AS_SET option has been configured |
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Command used to remove private ASs from the AS_PATH |
neighbor X.X.X.X remove-private-as configured in an outbound point of view (usually on the SP-edge, with the sp-core router being the X.X.X.X) |
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Responsible for the route filtering and manipulation: |
Input Policy Engine |
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When aggregating and using the AS_SET keyword, the following occurs: |
The path advertised for route will be an AS_SET consisting of all elements contained in all paths that have been summarized. |
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Command that lists possible routes per prefix |
show ip bgp prefix [subnet-mask] |
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BGP RIB-failure routes can be advertised to other neighbors. To stop this from happening, issue the following command: |
bgp suppress-inactive |
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Command used to change the default local preference |
bgp default local-preference |
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BGP AS-TRANS |
-Configured on a router that does not support 4 byte ASNs -Configure neighbors in a remote as (4 byte) with 23456 |
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What contents does the BGP consistency checker check? |
-Next-hop label - paths advertised by the same PE must have the same next-hop and next hop label -RIB-out - outbound routes must match the outbound policies -Aggregation - If specific routes and aggregate routes become out of sync, an inconsistency may occur |
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The no-export community attribute is nullified by- Use this community attribute instead- |
-confederations
-local-as (may also be nullified by the advertisement to ibgp confed peer, which then does not accept the community, therefore advertising the route to peers outside the confed) (be sure to send communities to confed peers) |
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Describe the function of BGP disable-connected-check |
-Does not check for "connected" route in routing table -Does not decrement TTL -Used to peer with a connected router's loopback |
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Three ways to filter routes from BGP neighbors: |
neighbor A.B.C.D prefix-list LIST [in|out] neihgbor A.B.C.D distribute-list LIST [in|out] neighbor A.B.C.D route-map MAP [in|out] |
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Disable bgp client-to-client reflection |
no bgp client-to-client reflection |
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By default, communities are stripped of outgoing BGP updates. This command propagates communities to BGP neighbors |
neighbor A.B.C.D send-community |
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The next-hop PA cannot be set through a route-map. What are the two methods of setting the next hop? |
iBGP - neighbor A.B.C.D next-hop-self eBGP - neighbor A.B.C.D next-hop-unchanged |
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Define Cluster List |
When a RR advertises a prefix to a non-client, it appends the cluster-id to the cluster list. |
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When using the neighbor A.B.C.D default-originate command, the following happens: |
A default route is advertised to those neighbors (without a default being defined). Use the route-map option to define a conditional default route. |
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If a route is not placed in the LOC-RIB, it cannot: |
Be placed in the ADJ-RIB-OUT for advertisement to peers |
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Command to list possible default routes |
show ip bgp 0.0.0.0 0.0.0.0 |
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When using the aggregate-address command, by default |
-The aggregate route will be advertised as coming from your AS and will have the atomic aggregate attribute set to show that information might be missing. -Use the keyword "as-set" to remove the atomic aggregate |
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This command forces a router to advertise itself as the next hop for the routes learned from a specific neighbor |
neighbor A.B.C.D next-hop-self |
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If the as-set option is used, and at least one of the component subnets has an ORIGIN code ?, the aggregate will have an origin code of: |
? |
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Routes that will be advertised to other BGP routers must be present in: Routes to be used by local BGP router must be present in: Routes received from other BGP routes must be present in: |
-Adj-RIB-out -Loc-RIB -Adj-RIB-in |
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This command tells the local router to proces prefixes with the local AS# in the prefix path |
neighbor A.B.C.D allowas-in |
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peer groups apply policies to - communities apply policies to - |
Peer groups- routers communities - routes |
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x.x.x.x from x.x.x.x (x.x.x.x) |
-Route -Neighbor IP -Neighbor RID |
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A Notification message is used to signal: |
A BGP error |
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BGP consistency checker will only take action when which keyword is used? |
auto-repair |
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A route-reflector and its clients are known as |
A cluster |
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Enable BGP consistency checker |
bgp consistency-checker {error-message | auto repair} [interval #minutes] |
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Capability codes reserved for vendor specific applications: |
128-255 |
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If a route is learned from a non-client iBGP peer, it is reflected to: |
clients only |
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NO_EXPORT |
A route carrying this community value should not be advertised to peers outside the AS |
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If a route is learned from an eBGP-peer, it is reflected to: |
Clients and non-clients |
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Use this command to assign a MED value of infinity to routes that are missing the MED attribute, making these paths the least desirable path: |
bgp bestpath med missing-as-worst |
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Reserved for use in documentation example code:
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192.0.2.0/24 |
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No-Advertise |
Should not be advertised to any BGP neighbor |
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No-Export |
Should not be advertised to an eBGP neighbor |
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If BGP neighbors have mismatched keepalive and hold timers, the neighbors will do the following: Default keepalive and hold timers: |
-Use the lower of the two -keepalive- 60 seconds, hold 180 seconds |
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Attributes not modified between Sub-AS's |
Next-hop, Local Pref, MED |
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A neighbor that is oscillating between connect and active, it is typically a sign of |
A TCP connection error (Too many TCP re-transmissions or inability to reach IP address) |
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When aggregating routes, use this keyword to suppress only specific routes |
Suppress-map |
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When in "connect" state, if the TCP transport connection is successful- If the transport connection is unsuccessful- |
-The state transitions into opensent -The state transitions into active |
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A BGP speaker determines the capabilities supported by other BGP speakers by the following action: |
BGP speaker examines the parameter of the OPEN message |
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Optional nontransitive |
When optional attribute is not recognized and the transitive flag is not set, the attribute should be ignored and not passed to its peers. -Originator_ID -Cluster List |
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-When a TCP transport disconnect is detected, the state falls back to: -For other errors, BGP sends: |
-The active state -A notification message (with corresponding error code) and falls back to the Idle state. |
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If a system propagates an aggregate that causes a loss of information, it is required to attach the: |
Atomic_Aggregate (well known, discretionary) |
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What BGP path attributes do route reflectors use to prevent loops? |
-Originator_ID -Cluster_List |
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MED's from different autonomous systems will not be compared unless- |
"bgp always-compare-med" command is specified
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Open message is used to establish ___, exchange basic ___, and exchange ___ |
-A neighbor relationship -Parameters -MD5 authentication |
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Command to list routes advertised to a neighbor after applying outbound filtering |
show ip bgp neighbors _IP_ADDRESS_ advertised-routes |
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What type of OSPF routes cannot be redistributed into BGP? |
External OSPF |
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BGP ASNs assignable by IANA for public use: |
1 - 64,495 |
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Displays routes matching the AS_PATH regular expression |
show ip bgp regexp _regexp_ |
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The AS_PATH path attribute consists of four different segments: |
-AS_SEQ -AS_SET -AS_CONFED_SEQ |
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An OPEN message is checked for correctness. AN error is found- |
The router sends a NOTIFICATION message and goes into IDLE |
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When redistributing BGP into an IGP, what must be understood? |
-When using "redistribute bgp" under any IGP process, only eBGP routes are redistributed. -To enable redistribution from iBGP, use "bgp redistribute internal" command |
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Multiprotocol Reachable NLRI (MP_REACH_NLRI) |
-Optional nontransitive attribute -Used to advertise a feasible route to a peer |
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List the number of prefixes learned per neighbor |
show ip bgp summary |
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Change the AD of routes received from a specific neighbor: Change the AD of specific routes received from a neighbor: |
-Distance AD# neighbor-ip wildcard-mask -Distance AD# neighbor-ip wildcard-mask ACL# |
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Command that lists routes learned from one neighbor before any route filtering is applied: |
Show ip bgp neighbors ip-address receive routes |
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AS_SET |
ASs that make up an aggregate are listed in an unordered set |
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Multiprotocol_Unreachable_NLRI (MP_UNREACH_NLRI) |
-Optional nontransitive -Used to withdraw one or more unfeasible routes from service |
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32 Byte AS Numbers can be written four different ways: |
-ASplain -ASdot+ -ASdot -AScolon |
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AS_PATH Considerations |
-Step #4 is skipped if bgp bestpath as-path ignore is configured -An AS_SET counts as 1, no matter how many ASs are in the set -The AS_CONFED_SEQUENCE and AS_CONFED_SET are not included in the AS_PATH length |
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Benchmark testing for internet (2544) |
198.18.0.0/15 |
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An update message will contain: |
-Network Layer Reachability Information -Path Attributes -Unfeasible Routes |
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ASN's reserved for use in documentation: |
64,496 - 64,511 |
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Default routes can be injected into BGP three ways: |
-network command -redistribution -neighbor neighbor-id default-originate [route-map _name_] |
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BGP fast external-fallover |
-If disabled, the routing process will wait until the hold timer expired before the peer session is reset, in the event of a failure -Only supports directly connected external peers -default is 180 seconds, or lowest negotiated |
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To cause the system to ignore the IGP metric during the BGP bestpath selection, use this command: |
bgp bestpath igp-metric ignore (address family configuration mode) |
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Optional Transitive- Optional Non-Transitive- |
-aggregator, community -MED |
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The BGP Loc-RIB contains: |
-Only preferred routes (Best routes after decision process) |
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When providers do not use manipulation techniques to prefer the best exit path, it is often referred to as: |
-Closest exit or hot potato routing |
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Well known communities: |
-Local-AS -No-Advertise -No-Export |
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Use this command to aggregate an entry in BGP: |
-Aggregate-address x.x.x.x _mask_ [as-set] [as-confed-set] [summary-only] |
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The only values that change when using the BGP confederations are: |
-AS_CONFED_SEQ -AS_CONFED_SET -The actual next-hop address |
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View the Originator_ID, Cluster/Cluster_ID, and cluster list: |
show ip bgp A.B.C.D |
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-Change the advertisement interval for a specific peer- -Internal and External defaults |
-neighbor A.B.C.D advertisement-interval # -External Peers - 30 seconds -Internal peers - 5 seconds |
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When routes containing the community attributes are aggregated, the aggregate: |
Inherits all the community attribute of all the routes |
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Four step tiebreaker process when choosing between multiple paths: |
1. Shortest AS_PATH 2.Prefer single eBGP route over multiple iBGP routes 3. If best route has still not been chosen, choose route with the lowest IGP next-hop metric 4. If IGP metric ties, use the iBGP route with lowest advertising RID |
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Cluster_ID |
-The RID of the route-reflector unless specifically configured otherwise |
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Local-AS works ___, No-Export does not. |
within a confederation |
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If the connect-retry timer expires, |
The state remains in the connect stage, the timer is reset, and a transport connection is initiated. |
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Command that lists routes learned from a specific neighbor that passed any inbound filters: |
show ip bgp neighbors x.x.x.x routes |
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The result of the network command with the keyword "backdoor"- |
Assigns an administrative distance of 200 to the network |
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AS_SET is made up of |
-AS_CONFED_SEQUENCE -AS_CONFED_SET |
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-AS_SET is defined by -Use this command to define the AS_SET segment in an aggregated subnet |
-AN unordered list of all AS's inherited from the aggregated routes -aggregate-address a.b.c.d mask summary-only as-set |
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ASN's for private use: |
64,512 - 65,534 |
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Route-reflector clients cannot be peered with |
-Routes outside their cluster |
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RT (Route-target) |
-64 bit extended BGP community that is attached to a VPNv4 BGP route to indicate its VPN membership -Any number of RTs can be attached to a single route |