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27 Cards in this Set
- Front
- Back
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Ingress LSR Process
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1. Routing lookup to determine outgoing int
2. If next hop label for destination exists: - impose label - change ethertype 3. Send labeled packet |
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MPLS Label Structure
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0-19: 20 bits - Label - values 0 - 15 are reserved
20-22: 3 bits - EXP 23: 1 bit - Bottom of Stack 24-31: 8 bits - TTL |
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Layer 2 PID/Ethertype 0x8847
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Labeled IP Unicast
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Layer 2 PID/Ethertype 0x8848
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Labeled IP Multicast
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Layer 2 PID/Ethertype 0x0800
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Unlabeled IP Unicast
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In the MPLS label structure, which labels are reserved?
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labels 0 through 15
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Which reserved label is used to indicate that the next-hop LSR should pop the label?
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label 3, displayed as imp-null in the LIB table
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Command: configure CEF
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Router(config)# ip cef
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Command: enable MPLS on an interface
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Router(config-if)# mpls ip
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Command: enable CEF on an interface after CEF has been disabled globally
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Router(config-if)# ip route-cache cef
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Command: enable dCEF (distributed CEF)
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Router(config)# ip cef distributed
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CEF is enabled by default on which platforms?
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- 7200
- 7100 - 7500 |
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dCEF is enabled by default on which platforms?
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- 6500
- 12000 |
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Command: turn on LDP
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On by default, when you turn on mpls ip on an interface. If you must re-enable it, do:
Router(config-if)# mpls label protocol ldp |
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Which label distribution protocol is the default on Cisco platforms: TDP or LDP?
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LDP is the default label distribution protocol
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ACL for filtering LDP traffic from customers
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ip access-list NoLDP deny udp any any eq 646
ip access-list NoLDP permit ip any any |
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Which port does LDP listen on?
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UDP 646
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MTU for bare or "pure" MPLS
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1504 bytes
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MTU for MPLS VPN
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1508 bytes (two labels)
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MTU for MPLS VPN with TE
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1512 bytes (three labels)
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Formula for full-mesh link count
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n * (n-1)
---------- 2 |
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Which protocol does MP-BGP use to keep customer routes separate from each other?
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VPNv4 for IPv4
VPNv6 for IPv6 Adds a 64-bit prefix called a Route Distinguisher to all customer routes |
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Which MPLS routers exchange VPNv4 addresses?
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Only the PE routers
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Command: force LDP to use loopback 0 as the LDP router ID
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Router(config)# mpls ldp router-id loopback0 force
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Command: create a VRF
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Router(config)# ip vrf <vrf-name>
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Command: assign an interface to a VRF
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Router(config-if)# ip vrf forwarding <vrf-name>
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Turn off MPLS TTL propagation
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Router(config)# no mpls ip propagate-ttl
OR Router(config)# no tag-switching ip propagate-ttl |
