Enhanced Interior Gateway Protocol
OSPF
EIGRP
Supports CIDR and VLSM, rapid
convergence, partial updates,
neighbour discovery
Supports CIDR and VLSM, rapid
convergence, partial updates,
neighbour discovery
Administrator can define route
summarization
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 balancing
Unequal-cost load balancing
Metric = 256*([K1*Bw + K2*Bw/(256-Load) + K3*Delay]*[K5/(Reliability + K4)]).


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
172.16.2.0/24
ISP
Loopback
10.1.1.1/30 .1
R2
172.16.3.0/24 S0/0/0
Fa0/0
172.16.1.0/24
.1
S0/0/0
DCE
.1
R1
.2
64 kbps
S0/0/1
.5
.9
S0/0/1
DCE
1024 kbps
1544 kbps
192.168.10.4/30
192.168.10.8/30
S0/0/1
.10
S0/0/0
DCE
.6
R3
Bandwidth = (10,000,000 / BW in kbps) x 256
•R2 Slowest Interface = S0/0/1 link at 1024kbps
•10,000,000 / 1024 = 9765.625
•Round Down = 9765
•9765 x 256 =2,499,840
Fa0/0
.1
192.168.1.0/24
172.16.2.0/24
ISP
Loopback
10.1.1.1/30 .1
R2
172.16.3.0/24 S0/0/0
Fa0/0
172.16.1.0/24
.1
S0/0/0
DCE
.1
.2
64 kbps
S0/0/1
R1
.5
.9
S0/0/1
DCE
1024 kbps
1544 kbps
192.168.10.4/30
192.168.10.8/30
S0/0/1
.10
S0/0/0
DCE
.6
R3
Fa0/0
.1
192.168.1.0/24
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
5
172.16.2.0/24
ISP
Loopback
10.1.1.1/30 .1
R2
172.16.3.0/24 S0/0/0
Fa0/0
172.16.1.0/24
.1
S0/0/0
DCE
.1
R1
.2
64 kbps
S0/0/1
.5
.9
S0/0/1
DCE
1024 kbps
1544 kbps
192.168.10.4/30
192.168.10.8/30
S0/0/1
.10
S0/0/0
DCE
.6
R3
Calculate the metric to reach destination 192.168.1.0/24 from R1
Metric = [K1 x bandwidth (min) + K3 x delay (cumulative)]
Fa0/0
.1
192.168.1.0/24
•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.
10
R2
15
R1
10
Router
RD/AD
FD
R2
10
20
R3
10
25
R4
30
45
FC = RD<FD
10
R3
R5
192.168.10.0/24
15
30
R4
•Successor = R2 (FD=20)
•Feasible Successor = R3 (10<20)
•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.
10
Update
R2
10
Router
RD/AD
FD
R2
10
20
R3
10
25
R4
30
45
ACK
15
R1
FC = RD<FD
10
R3
R5
192.168.10.0/24
Update
15
30
R4
ACK
•Successor = R3 (FD=25)
•No Feasible Successor = R3 (30>25)
•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.
R2
15
R1
10
Router
RD/AD
FD
R2
10
20
R3
10
25
R4
30
45
FC = RD<FD
10
R3
R5
192.168.10.0/24
Query
15
30
R4
Reply
•Successor = R4 (FD=45)
•No Feasible Successor




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.
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
10
R2
15
R1
10
Router
RD/AD
FD
R2
10
20
R3
10
25
R4
30
45
FC = RD<FD
10
R3
R5
192.168.10.0/24
15
30
R4
R1(config)#router eigrp 1
R1(config-router)#variance 2


How will R1 route
packets to R2’s
loopback interface?
Issues if R1 uses both
direct path and and
indirect path using R3?
Routing Loops
Unequal cost paths

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.
10.1.1.0/24

Hub Network
A
B
Router B
Router A
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.
Spoke 4
Spoke 3
Spoke 2
Spoke 1
Not Designed to
Transit Traffic

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.
10.1.1.0/24
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:
Hub Network
Reply
Query
B
A
Router A
Router B
Spoke 4
Spoke 3
Spoke1(config)router eigrp 100
Spoke1(config-router)#eigrp stub
Spoke 2
Spoke 1
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
Eigrp stub configuration need only be entered on the
spoke routers.
Router(config-router)#eigrp stub
[receive-only|connected|static|summary]





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.
Update: C- 2.0.0.0/8
C –2.0.0.0/8
Subnet 2.1.1.0/24
C – 2.0.0.0/8
Subnet 2.2.2.0/24
•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.
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.
•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.
172.16.2.0/24
ISP
Loopback
10.1.1.1/30 .1
R2
172.16.3.0/24 S0/0/0
Fa0/0
172.16.1.0/24
.1
S0/0/0
DCE
.1
R1
.2
64 kbps
S0/0/1
.5
.9
S0/0/1
DCE
1024 kbps
1544 kbps
192.168.10.4/30
192.168.10.8/30
192.168.1.0/24
S0/0/1
.10
S0/0/0
DCE
.6
R3
Fa0/0
.1
Lo2
192.168.2.1/24
Lo2
192.168.3.1/24



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 128
R1(config-if)#ip bandwidth-percentage eigrp 1 25
AS
%

Simple password authentication:

MD5 authentication
◦ Router sends packet and key.
◦ Neighbor checks if received key matches its key.
◦ Not secure.
◦ 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.
R1(config)#interface Serial0/0/1
R1(config-if)#bandwidth 64
R1(config-if)# ip address 192.168.1.101 255.255.255.224
R1(config-if)# ip authentication mode eigrp 100 md5
R1(config-if)# ip authentication key-chain eigrp 100 R1chain
R1(config)# key chain R1chain
R1(config-keychain)#key 1
R1(config-keychain-key)#key-string firstkey
R1(config-keychain-key)# accept-lifetime 04:00:00 Jan 1 2006 infinite
R1(config-keychain-key)# send-lifetime 04:00:00 Jan 1 2006 04:30:00 Jan 1 2006
R1(config-keychain)# key 2
R1(config-keychain-key)#key-string secondkey
R1(config-keychain-key)#accept-lifetime 04:00:00 Jan 1 2006 infinite
R1(config-keychain-key)#send-lifetime 04:29:00 Jan 1 2006 infinite