OSPF/MPLS Assignment

HW1-w16-ans-UPDATE.pdf

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NOTE: I am providing you these answers from HW #1 to help you with answering the similar questions on the Winter 2019 HW #1 assignment.

160.2.0.0/16

Subnet

R1 R2 R3

Fa0/0 Fa0/0S0/1S0/0S0/1S0/1 140.1.0.0/24

LoopBack0 50.1.1.1

LoopBack0 50.1.1.3

LoopBack0 50.1.1.2

Subnet S0/0 S0/0

Link 1 256 Kbps

Link 2 1 Mbps

Link 3 1 Mbps

Router Interface IP Router Interface IP Router Interface IP

R1 Fa0/0 140.1.0.1 R1 S0/0 30.0.0.9 R1 S0/1 30.0.0.1 R2 S0/0 30.0.0.5 R2 S0/1 30.0.0.2 R3 Fa0/0 160.2.1.1 R3 S0/0 30.0.0.10 R3 S0/1 30.0.0.6 R1 Lo0 50.1.1.1 R2 Lo0 50.1.1.2 R3 Lo0 50.1.1.3

1. Consider the network above. R1, R2 and R3 are MPLS Label Switched Routers (LSRs). They use OSPF as IGP and LDP for label distribution. These LSRs use per-platform label space, unsolicited downstream label distribution, liberal label retention mode. Each router has a /32 LoopBack0 address that is used as its LSR ID. The three serial links are /30 subnets. The interface IP addresses are shown in the address table. Assume OSPF has converged so all routing tables are up-to-date. The Bandwidth values shown on the 3 serial links determine their OSPF link costs. The OSPF link cost for a Loopback interface is 1. a) (7 points) Show me the contents of the Router R1 Routing Table. Your routing table

should have 5 columns, labeled Subnet ID, Mask, OSPF Cost, Next Hop, Outgoing Interface and 8 rows, corresponding to the 8 IP subnets in the diagram (including Loopback0s). Each Next Hop value will either be an IP address or blank.

2. Now the three routers assign Local Labels to each subnet in their routing tables as follows. Assume that PHP is not used.

R1 Routing Table

Subnet ID Mask OSPF Cost Next Hop Outgoing Interface

30.0.0.0/30 255.255.255.252 -- -- S0/1 30.0.0.4/30 255.255.255.252 200 30.0.0.10 S0/0 30.0.0.8/30 255.255.255.252 -- -- S0/0 50.1.1.1/32 255.255.255.255 -- -- Loopback0 50.1.1.2/32 255.255.255.255 201 30.0.0.10 S0/0 50.1.1.3/32 255.255.255.255 101 30.0.0.10 S0/0

140.1.0.0/24 255.255.255.0 -- -- Fa0/0 160.2.0.0/16 255.255.0.0 101 30.0.0.10 S0/0

a) (7 points) Now the LDP protocol executes so the Label Information Base (LIB) tables on all routers are up to date. As in the class example on slide #29, show me the contents of the Router R1 LIB. Your LIB table should have 4 columns labeled FEC, Local Label, Remote Label, Remote LSR ID. Unlike the class example, your LSR IDs must be IP addresses. Assume that PHP is not used.

b) (7 points) Based on values in its Routing Table and LIB, each router now computes its Label Forwarding Information Base (LFIB). As in the class example on slide #30, show me the contents of the Router R1 LFIB. Your LFIB table should have 6 columns labeled Incoming Label, Action, Outgoing Label, FEC, Outgoing Interface, Next Hop. Unlike in the class example, your Next Hop must be an IP address or blank. Assume that PHP is not used.

Subnet R1 Local

Label R2 Local

Label R3 Local

Label 30.0.0.0/30 40 60 90 30.0.0.4/30 41 61 91 30.0.0.8/30 42 62 92 50.1.1.1/32 43 63 93 50.1.1.2/32 44 64 94 50.1.1.3/32 45 65 95

140.1.0.0/24 46 66 96 160.2.0.0/16 47 67 97

R1 Label Information Base (LIB)

FEC Local Label Remote Label

Remote LSR ID

30.0.0.0/30 40 60 50.1.1.2 30.0.0.0/30 40 90 50.1.1.3 30.0.0.4/30 41 61 50.1.1.2 30.0.0.4/30 41 91 50.1.1.3 30.0.0.8/30 42 62 50.1.1.2 30.0.0.8/30 42 92 50.1.1.3 50.1.1.1/32 43 63 50.1.1.2 50.1.1.1/32 43 93 50.1.1.3 50.1.1.2/32 44 64 50.1.1.2 50.1.1.2/32 44 94 50.1.1.3 50.1.1.3/32 45 65 50.1.1.2 50.1.1.3/32 45 95 50.1.1.3

140.1.0.0/24 46 66 50.1.1.2 140.1.0.0/24 46 96 50.1.1.3 160.2.0.0/16 47 67 50.1.1.2 160.2.0.0/16 47 97 50.1.1.3

c) (5 points) Now, using LFIB from #2(b), consider a packet sent by R1 to destination 50.1.1.2. This packet will go over Link 3 and Link 2. i) What MPLS label value, if any, will be in the header of this packet as it passes over

Link 3? 94 ii) What MPLS label value, if any, will be in the header of this packet as it passes over

Link 2? 64 3. Now we will go back and repeat the steps of problem #2 assuming that PHP is used.

a) (6 points) When PHP is active, the assignment of Local Labels will be different than the Local Label table shown in problem #2, because IMP-NULL values will be in the Local Label table. Show me a feasible Local Label table (4 columns, 8 rows) that assigns local labels to each of the 8 subnets on R1, R2 and R3 when PHP is used.

b) (6 points) Using your Local Label table from answer #3(a), now go back and repeat the building of the LIB as in problem #2(a) assuming that PHP is used. Write out the contents of the Router R1 LIB using PHP.

R1 LFIB Incoming

Label Action Outgoing

Label FEC Outgoing

Interface Next Hop

40 POP -- 30.0.0.0/30 S0/1 -- 41 SWAP 91 30.0.0.4/30 S0/0 30.0.0.10 42 POP -- 30.0.0.8/30 S0/0 -- 43 POP -- 50.1.1.1/32 Loopback0 -- 44 SWAP 94 50.1.1.2/32 S0/0 30.0.0.10 45 SWAP 95 50.1.1.3/32 S0/0 30.0.0.10 46 POP -- 140.1.0.0/24 Fa0/0 -- 47 SWAP 97 160.2.0.0/16 S0/0 30.0.0.10

Subnet R1 Local

Label R2 Local

Label R3 Local

Label 30.0.0.0/30 IMP-NULL IMP-NULL 90 30.0.0.4/30 40 IMP-NULL IMP-NULL 30.0.0.8/30 IMP-NULL 60 IMP-NULL 50.1.1.1/32 IMP-NULL 61 91 50.1.1.2/32 41 IMP-NULL 92 50.1.1.3/32 42 62 IMP-NULL

140.1.0.0/24 IMP-NULL 63 93 160.2.0.0/16 43 64 IMP-NULL

c) (7 points) Now, using the routing table you got in #1(a) and the LIB from #3(b) show the contents of the Router R1 LFIB, assuming that PHP is used.

d) (5 points) Now, using LFIB from #3(c), consider a packet sent by R1 to destination 50.1.1.2. i) What MPLS label value, if any, will be in the header of this packet as it passes over

Link 3? 92 ii) What MPLS label value, if any, will be in the header of this packet as it passes over

Link 2? No Label

R1 Label Information Base (LIB)

FEC Local Label Remote Label

Remote LSR ID

30.0.0.0/30 Imp-NULL Imp-NULL 50.1.1.2 30.0.0.0/30 Imp-NULL 90 50.1.1.3 30.0.0.4/30 40 Imp-NULL 50.1.1.2 30.0.0.4/30 40 Imp-NULL 50.1.1.3 30.0.0.8/30 Imp-NULL 60 50.1.1.2 30.0.0.8/30 Imp-NULL Imp-NULL 50.1.1.3 50.1.1.1/32 Imp-NULL 61 50.1.1.2 50.1.1.1/32 Imp-NULL 91 50.1.1.3 50.1.1.2/32 41 Imp-NULL 50.1.1.2 50.1.1.2/32 41 92 50.1.1.3 50.1.1.3/32 42 62 50.1.1.2 50.1.1.3/32 42 Imp-NULL 50.1.1.3

140.1.0.0/24 Imp-NULL 63 50.1.1.2 140.1.0.0/24 Imp-NULL 93 50.1.1.3 160.2.0.0/16 43 64 50.1.1.2 160.2.0.0/16 43 Imp-NULL 50.1.1.3

R1 LFIB Incoming

Label Action Outgoing

Label FEC Outgoing

Interface Next Hop

40 POP -- 30.0.0.4/30 S0/0 30.0.0.10 41 SWAP 92 50.1.1.2/32 S0/0 30.0.0.10 42 POP -- 50.1.1.3/32 S0/0 30.0.0.10 43 POP -- 160.2.0.0/16 S0/0 30.0.0.10