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41 Cards in this Set
- Front
- Back
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What are MPLS protocols? |
LDP and RSVP-TE |
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What are MPLS applications? |
MPLS label switching, MPLS L2 and L3 VPNs, |
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What is MPLS header located? MPLS Label Format? |
Between L2 and l3. 4 byte total . 20 bit label, 3 bit EXP, S bit (last label in stack), and 8 bit TTL. |
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What are the MPLS label 3 and 0? |
3 is implicit null - signals to upstream to remove the label because I will switch out non MPLS interface - PHP |
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What is a remote label and local label? |
Remote is a label that is advertised to me and local is label that advertise for the FEC. If a packet comes with local label I know to swap to the remote lab. |
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What are the label operation and meanings? |
Push - means to add a label Pop - means to remove a label Swap - means to change a label |
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What is a FEC and how does it relate to labels? |
An FEC is a route. And every FEC gets a locally assigned label. |
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What protocol advertises labels? What TCP/UDP port? What address does it use? Does it make labels for IGP and BGP routes? Who initiates? |
LDP, 224.0.0.2 (all routers), UDP 646 until finds router and then TCP 646 between Router ID. It only creates labels for IGP, static, connected. Router with highest LDP RID |
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How LDP ID defined? mpls ldp discovery transport-address interface | A.B.C.D |
LDP RID is static, high loopback, then high non loopback Changes the address for LDP neighbors. The LDP transport address is a field in the LDP discovery packet. When a device sees it it communicates to this address via TCP. |
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How can have a no route problem with LDP? |
LDP peers are established with the transport address which is the router id. The Router ID must be in the IGP or you will see neighbor with xmit/recv LDP xxxxx:0; no route |
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What is the RIB? What are the two tables created for CEF? What in the tables? |
Routing Information Base aka Route Table. Forwarding Information Base and Adjacency Table. FIB has routes from route table with next-hop. Adjacency includes the layer 2 information. |
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All labels are shared but are all used? What table are they stored in? |
Not all labels are used. They are actually shared for FEC belonging to neighbor who told me about that FEC. The table holding all lables is the Lable Information Base. show mpls label bindings |
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What table shows what labels are actually used? How we determine which to use? What is done with the best label? |
The LFIB. IGP determines next-hop. Each LDP neighbor shares the local interfaces. So we use the label associated with the LDP neighbor holding the next-hop. show mpls forwarding x.x.x.x Best label is placed in FIB and LFIB |
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mpls ip propagate-ttl does what? What does disabling this do? What is the default? Where does it need to be configured? |
This command will copy the TTL from the IP packet and continue to decrement as it crosses the network. Once it arrives on the other side the TTL is copied to the IP packet. The SP network is also revealed with traceroute. Disabling would cause router to not copy IP and add a new 255 on the MPLS header. It would mask the network from traceroute. This is on by default Only on PE routers. |
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mpls ip propagate-ttl no mpls ip propagate-ttl forwarded |
The no forwarded would allow PE router to copy TTL from IP packets locally generated but not forwarded packets. |
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mpls ip propagate-ttl no mpls ip propagate-ttl local |
The no local would not copy for router but copy from forwarded packets. |
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Label Static Applications? How do you know this is last label in stack? |
RSVP-TE LSP with LDP LSP inside of it. The S-bit is set. |
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What is an LSP for LDP? |
It is a dynamically signalled switching path between to LSRs. |
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What is the problem with regular Ping and Traceroute for MPLS? |
If LSP is broken in a standard MPLS network the devices will simply use RIB to route packet. Ping for VPNv4 will not tell where it is broken it will just fail. Traceroute for standard MPLS will also not show broken LSP. Traceroute for VPNv4 will stop of PE if LSP is broken. |
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What has been added to MPLS ping and traceroute to work? Where can it be used? |
Packet is not an ICMP packet. It can only be used on LSR. Source is the source rtr, dest IP is loopback. UDP is 3503. IP TTL is 1. MPLS Label is from FEC which is pinged. IP Router Alert Set header to packet is processed by RP. When packet arrives at P router it will continue down LSP. For traceroute the MPLS TTL follows normal traceroute behavior. |
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what is MRU? traceroute mpls ipv4 10.1.1.1/32 Type escape sequence to abort. 0 10.0.23.2 MRU 1500 [Labels: 32 Exp: 0] I 1 10.0.23.3 MRU 1504 [Labels: implicit-null Exp: 0] 8 ms ! 2 10.0.13.1 20 ms |
MTU |
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what is force-explicit-null? traceroute mpls ipv4 10.1.1.1/32 force-explicit-null Type escape sequence to abort. 0 10.0.23.2 MRU 1500 [Labels: 32 Exp: 0] I 1 10.0.23.3 MRU 1504 [Labels: implicit-null Exp: 0] 8 ms ! 2 10.0.13.1 20 ms |
This adds explicit null to bottom of label stack forcing the PHP to not happen an verify label switching on the last segment. |
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What is TTL1 for? And dsmap? ping mpls ipv4 10.1.1.1/32 ttl 1 dsmap L Echo Reply received from 10.0.23.3 DSMAP 0, DS Router Addr 127.0.0.1, DS Intf Addr 0 Depth Limit 0, MRU 1504 [Labels: implicit-null Exp: 0] Multipath Addresses: |
TTL 1 is MPLS TTL 1 and forces packet to stop at next-hop and performs a downstream-map of that router. |
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With MPLS what would happen if you configure an iBGP neighbor on PE routers and use loopback advertised in IGP as update source? |
This is the first building blocks to L3VPNs. In PE route table the next-hop for the BGP routes is the update source of the neighbor. This next-hop is available through an LSP aka label. So all BGP routes would show a next-hop which all of the same label. This is referred to as the transport label in L3VPNs. |
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How to go from iBGP with MPLS BGP free core to MPBGP with BGP free core? |
The iBGP neighbor would just need to add the VPNv4 address family to transport the routes across the core. router bgp 100 neighbor 1.1.1.1 remote-as 100 neighbor 1.1.1.1 update-source lo0 address-family vpnv4 unicast neighbor 1.1.1.1 activate neighbor 1.1.1.1 send-community extended |
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What is next step to creating VPNv4 routes? Where do they came from? What does the BGP update look like |
Creating a vrf and address family vrf inside of BGP. Those routes will be automatically added to the VPNv4. It will include the RD, RT, network prefix and infamous VPN Label. Router bgp 1 address-family ipv4 vrf CustomerB redistribute rip |
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What does the vrf and BGP vrf config look like? |
ip vrf CustomerA rd 1:100 route-target export 1:10 router-target import 1:30 Ip route vrf CustomerA 10.10.10.0 255.255.255.0 172.16.1.1 ! Router bgp 1 address-family ipv4 vrf CustomerA redistribute connected redistribute static |
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What is purpose of RD? |
The VPNv4 routes for all customers will go into a shared VPNv4 table. The RD makes the routes unique in case the customer's are using same IP address. |
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What is the purpose of route target? |
This tells BGP what routes to dump into each VRF. |
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mpls labels in/out nolabel/25 what does this mean at the end of a VPNv4 route? |
25 means this is the outgoing label which the remote PE should use as the VPN label. |
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How to get CE routing protocols into VPNv4 table? |
The CE protocol must be configured in the VRF. The BGP address family VRF must redistribute that protocol. |
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What does basic RIP look like? |
Router rip address-family ipv4 vrf RED version 2 no auto-summary network 192.168.0.0 redistribute bgp 1 metric transparent router bgp 200 address-family ipv4 vrf RED redistribute rip |
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What does basic EIGRP look like in classic? |
Router eigrp 65001! ASN used by ISP address-family ipv4 vrf CustomerB autonomous-system 1 redistribute bgp 100 metric 1 1 1 1 1 ! Router bgp 1 address-famly ipv4 vrf CustomerB redistribute eigrp 1 |
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What is EIGRP Cost Community and SOO? |
Used for site with backdoor to prevent loops. |
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What does this command do? router ospf x vrf xxx. If VRF is extended to CE router what command is needed to stop PE checks. |
Cause OSPF to believe it is connected to a super backbone. It will perform PE check to a reject all non-zero area summaries. capability vrf-lite |
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If process ID and domain ID are the same what happens to the type 1,2, and 5 LSA router ospf 100 vrf xxx domain-id xxxxxx |
It will change Type 1 and 2 to a summary and keep 5 the same. |
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If process ID and domain ID are different happens to the type 1,2, and 5 LSA router ospf 100 vrf xxx domain-id xxxxxx |
It will send them all as external LSA. |
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What does PE added to Type 3 and Type 5 to prevent loops on backdoors? |
DN bit on Type 3 and BGP AS and Path length in type 5. If PE on other end of backboor AS or DN bit it will drop. |
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VRF lite config for EIGRP with classic mode? |
Ip vrf xx rd x:x! Interface x/x ip vrf forward x/x! Router eigrp xx address family ipv4 vrf xx autonomous-system xx network xxx no auto-summary |
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How to configure internet access? |
The PE VRF needs route to default pointing to global VRF. ip route vrf VPN_A 0.0.0.0 0.0.0.0 [next-hop] global The PE global needs route pointing to customer network with next-hop and interface. ip route 11.11.11.0 255.255.255.0 Serial8/0 192.168.10.1 |
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MPLS session protection? |
MPLS session tunnel protection - Session protection for LDP maintains LDP session for neighbor via targeted LDP session when if link fails and there is another IGP route. The duration says how long to hold and for an ACL can be given for which LDP neighborsmpls ldp session protection [for acl] [duration seconds] |
