EIGRPEnhanced Interior Gateway Protocol

OSPF EIGRP

Supports CIDR and VLSM, rapidconvergence, partial updates, neighbour discovery

Supports CIDR and VLSM, rapidconvergence, partial updates, neighbour discovery

Administrator can define routesummarization

Automatic route-summarization and user defined route summaries

Open standard; multivendor support

Proprietary; Cisco routers only

Scalable; administratively defined“areas” provide manageable hierarchy

Scalable, but no hierarchical design

Difficult to implement Easy to implement

Equal-cost load balancingUnequal-cost load balancing

OSPF vs EIGRP

EIGRP Metric calculation

Default constant values:- K1=1, K2=0, K3=1, K4=0, K5=0

Metric = [K1 x bandwidth (min) + K3 x delay (cumulative)]

The default K values can be changed with the EIGRP router command:

R2(config-router)# metric weights tos k1 k2 k3 k4 k5

Metric = 256*([K1*Bw + K2*Bw/(256-Load) + K3*Delay]*[K5/(Reliability + K4)]).

Bandwidth Metric Calculation

S0/0/0 S0/0/1DCE

R2

R1

S0/0/0DCE

S0/0/1

192.168.10.8/30

172.16.2.0/24

192.168.1.0/24R3172.16.1.0/24

Fa0/0 Fa0/0

172.16.3.0/24

.1

.1

.2 .9

.10

.1

.1S0/0/1

.5192.168.10.4/30

S0/0/0DCE .6

64 kbps 1024 kbps

1544 kbps

ISP Loopback10.1.1.1/30

•R2 Slowest Interface = S0/0/1 link at 1024kbps•10,000,000 / 1024 = 9765.625

•9765 x 256 =2,499,840

•Round Down = 9765

Bandwidth = (10,000,000 / BW in kbps) x 256

5

Delay Metric Calculation

S0/0/0 S0/0/1DCE

R2

R1

S0/0/0DCE

S0/0/1

192.168.10.8/30

172.16.2.0/24

192.168.1.0/24R3172.16.1.0/24

Fa0/0 Fa0/0

172.16.3.0/24

.1

.1

.2 .9

.10

.1

.1S0/0/1

.5192.168.10.4/30

S0/0/0DCE .6

64 kbps 1024 kbps

1544 kbps

ISP Loopback10.1.1.1/30

Delay = (Sum of delay / 10) x 256

•Sum = 100 + 20,000 = 20,100uS

•Sum /10 = 20,100 / 10 = 2,010

•2,010 x 256 = 514,560

Composite Metric Calculation

S0/0/0 S0/0/1DCE

R2

R1

S0/0/0DCE

S0/0/1

192.168.10.8/30

172.16.2.0/24

192.168.1.0/24R3172.16.1.0/24

Fa0/0 Fa0/0

172.16.3.0/24

.1

.1

.2 .9

.10

.1

.1S0/0/1

.5192.168.10.4/30

S0/0/0DCE .6

64 kbps 1024 kbps

1544 kbps

ISP Loopback10.1.1.1/30

Calculate the metric to reach destination 192.168.1.0/24 from R1Metric = [K1 x bandwidth (min) + K3 x delay (cumulative)]

Convergence -The Diffusing Update Algorithm (DUAL)

R1 R3 R5

R4

R2 10

10

30

10

15

15

192.168.10.0/24

Router RD/AD FD

R2

R3

R4

10

10

30

20

25

45

FC = RD<FD

•The feasibility condition (FC) is met when a neighbor's reported distance (RD) to a network (192.168.10.0/24) is less than the local router's feasible distance (FD) to the same destination network.

•Successor = R2 (FD=20)

•Feasible Successor = R3 (10<20)

Convergence - The Diffusing Update Algorithm (DUAL)

R1 R3 R5

R4

R2 10

10

30

10

15

15

192.168.10.0/24

Router RD/AD FD

R2

R3

R4

10

10

30

20

25

45

FC = RD<FD

•If the Successor route fails, R1 will immediately enter the feasible successor into the routing table. •R1 will update it’s neighbours about the topology change.

•Successor = R3 (FD=25)

•No Feasible Successor = R3 (30>25)

Update

Update

ACK

ACK

Convergence/Fault Tolerance - The Diffusing Update Algorithm (DUAL)

R1 R3 R5

R4

R2 10

10

30

15

15

192.168.10.0/24

Router RD/AD FD

R2

R3

R4

10

10

30

20

25

45

FC = RD<FD

•If the new successor route fails, R1 no longer has a feasible successor, so it enters the Active state. •R1 will now query it’s neighbours for a route to network 192.168.10.0/24.

•Successor = R4 (FD=45)

•No Feasible Successor

Query

Reply

Equal Cost Load Balancing Equal-cost load balancing is the ability of a router to

distribute traffic over all its network ports that are the same metric from the destination address.

EIGRP automatically load balances across equal cost paths. Load balancing increases the use of network segments and increases effective network bandwidth.

Cisco IOS software by default will install up to four equal-cost paths in the routing table for most routing protocols.

The maximum-paths command in can be used to allow up to six equal-cost paths.

R1 R3 R5

R4

R2 10

10

30

10

15

15

192.168.10.0/24

Router RD/AD FD

R2

R3

R4

10

10

30

20

25

45

FC = RD<FD

Equal Cost Load Balancing•EIGRP can also balance traffic across multiple routes that have different metrics, which is called unequal-cost load balancing. •The degree to which EIGRP performs load balancing is controlled with the variance command

R1(config)#router eigrp 1R1(config-router)#variance 2

Unequal Cost Load Balancing-Routing Loops

Routing Loops Unequal cost paths

How will R1 route packets to R2’s loopback interface?

Issues if R1 uses both direct path and and indirect path using R3?

Scalability – Limiting Queries: Hub & Spoke Network

The spoke routers are remotes sites, and they have two connections for redundancy, not so they can transit traffic between Router A and Router B.

Router A should never use the spokes as a path to anything reachable through Router B, so there’s no reason to learn about, or query for, routes through these spokes.

BA

10.1

.1.0

/24

Not Designed to Transit Traffic

Hub Network

Spoke 1

Spoke 2

Spoke 3

Spoke 4

Router A Router B

Scalability – Limiting Queries:EIGRP Stub Routing

The EIGRP Stub Routing feature:◦ Improves network stability◦ Reduces resource utilization and◦ Simplifies remote router (spoke) configuration

Stub routing is commonly used in hub-and-spoke topology.

Stub router sends a special peer information packet to all neighboring routers to report its status as a stub router.

Any neighbor that receives a packet informing it of the stub status does not query the stub router for any routes.

BA

10.1

.1.0

/24 Hub Network

Spoke 1

Spoke 2

Spoke 3

Spoke 4

Router A Router B

Scalability – Limiting QueriesEIGRP Stub Routing

Spoke1(config)router eigrp 100Spoke1(config-router)#eigrp stub

To inform Routers A & B B that the paths through the spokes should not be used for transit traffic, the spoke routers can be configured as stubs:

QueryReply

EIGRP- Issues with redundant network

Can you identify problems with reudundancy in the network

Several solutions to problem in the last slide: Add a redundant Ethernet link between routers

A and B to contain the backbone traffic to the hub site

Use some level of route summarization to limit the extents of the EIGRP QUERY mechanism.

Configure a distribute-list to limit the networks advertised by the spoke routers.

Best Solution: is to control traffic flows and limit query depth using EIGRP Stub Router functionality

Solution- EIGRP- Issues with redundant network

Configuring EIGRP Stub

receive-only: Prevents the stub from sending any type of route. connected: Permits stub to send connected routes (may still

need to redistribute). static: Permits stub to send static routes (must still

redistribute). summary: Permits stub to send summary routes. Default is connected and summary.

Eigrp stub configuration need only be entered on the spoke routers.

Router(config-router)#eigrp stub [receive-only|connected|static|summary]

Automatic Summarisation

•EIGRP automatically summarises routes at the classful boundary—the boundary where the network address ends as defined by class-based addressing.

•In most cases, auto summarisation is beneficial, because it keeps the routing tables as compact as possible.

•Auto summarisation causes problems when two subnets are discontiguous.

C –2.0.0.0/8 Subnet 2.1.1.0/24

C – 2.0.0.0/8Subnet 2.2.2.0/24

Update: C- 2.0.0.0/8

EIGRP automatically includes a null0 summary route as a child

route whenever both of following conditions exist:

1. There is at least one subnet that was learned via EIGRP.

2. Automatic summarisation is enabled.

Null0 Summary Route

Null0 Summary Route•EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes.

•Even with classless routing behavior configured, where the route lookup process will check for supernets and default routes, EIGRP will use the Null0 summary route and discard the packet because this route will match any packets of the parent that do not have a child route.

Lo2192.168.2.1/24

Performance - EIGRP Manual Summarisation

S0/0/0 S0/0/1DCE

R2

R1

S0/0/0DCE

S0/0/1

192.168.10.8/30

172.16.2.0/24

192.168.1.0/24

R3172.16.1.0/24

Fa0/0 Fa0/0

172.16.3.0/24

.1

.1

.2 .9

.10

.1

.1S0/0/1

.5192.168.10.4/30

S0/0/0DCE .6

64 kbps 1024 kbps

1544 kbps

ISP Loopback10.1.1.1/30

Lo2192.168.3.1/24

Bandwidth Optimisation- Configuring WAN Links By default, EIGRP may use up to 50 % of the

bandwidth of an interface or sub-interface for routing traffic.

EIGRP uses the bandwidth specified with the bandwidth command, or the default bandwidth of the link if none is configured, when calculating how much bandwidth to use.

EIGRP bandwidth usage can be adjusted as follows:R1(config)#interface s0/0/0

R1(config-if)#bandwidth 128R1(config-if)#ip bandwidth-percentage eigrp 1 25

AS %

Security :Simple Password vs. MD5 Authentication

Simple password authentication:◦ Router sends packet and key.◦ Neighbor checks if received key matches its key.◦ Not secure.

MD5 authentication◦ Configure a “key” (password) and key-id; router

generates a message digest, or hash, of the key, key-id and message.

◦ Message digest is sent with packet; key is not sent.◦ Secure.

Security - EIGRP MD5 Authentication Configuration

R1(config)#interface Serial0/0/1R1(config-if)#bandwidth 64R1(config-if)# ip address 192.168.1.101 255.255.255.224R1(config-if)# ip authentication mode eigrp 100 md5R1(config-if)# ip authentication key-chain eigrp 100 R1chain

R1(config)# key chain R1chainR1(config-keychain)#key 1R1(config-keychain-key)#key-string firstkeyR1(config-keychain-key)# accept-lifetime 04:00:00 Jan 1 2006 infiniteR1(config-keychain-key)# send-lifetime 04:00:00 Jan 1 2006 04:30:00 Jan 1 2006 R1(config-keychain)# key 2R1(config-keychain-key)#key-string secondkeyR1(config-keychain-key)#accept-lifetime 04:00:00 Jan 1 2006 infiniteR1(config-keychain-key)#send-lifetime 04:29:00 Jan 1 2006 infinite