EIGRP over Frame relay

As i continuing my journey towards my ccnp route i made a lab to test my skills in EIGRP over the frame relay  networks

First when i configured i got two problems to get the full convergence over frame-relay so i had to read a little bit more about the frame-relay.The two issues are

Split Horizon: Don't send the route update on the same interface it has received on.

In frame relay HUB and SPOKE setup the spoke to spoke communication happen through HUB so if there are any networks behind SPOKES those networks cannot be sent to other spoke because of split horizon.so i disabled this both on interface and subinterface of  HUB.

HUB:
interface Serial0/1
 no ip address
 encapsulation frame-relay
 no ip split-horizon eigrp 90
!
interface Serial0/1.1 multipoint
 ip address 10.2.0.1 255.255.255.248
 no ip split-horizon eigrp 90



EIGRP sends "HELLO" on every 60 seconds on frame relay network and 3 times of it is "HOLD DOWN" timer which is 180 seconds and these "HELLO's" are sent to multicast address "224.0.0.10" we know that frame-relay is "non-broadcast multiple access(NBMA)" which it doesn't allow broadcast or multicast address so it uses "pseudo broadcast"which a kind of broadcast which mainly depends on frame-relay map commands.

So while configuring frame relay maps make sure that all the commands ends with broadcast.

EXAMPLE:
frame-relay map ip 10.2.0.2 102 broadcast
frame-relay map ip 10.2.0.3 103 broadcast

If we dont configure with broadcast word at the end of the frame-relay map then router adjacency flaps.i removed  "frame-relay map ip 10.2.0.3 103 broadcast" map command on HUB and configured as "frame-relay map ip 10.2.0.3 103" and you will observe the following error.

*Mar  1 00:23:34.131: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 90: Neighbor 10.2.0.3 (Serial0/1.1) is down: retry limit exceeded
HUB#
*Mar  1 00:23:38.319: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 90: Neighbor 10.2.0.3 (Serial0/1.1) is up: new adjacency

configurations

HUB:
interface Serial0/1
 no ip address
 encapsulation frame-relay
 no ip split-horizon eigrp 90
 serial restart-delay 0
!
interface Serial0/1.1 multipoint
 ip address 10.2.0.1 255.255.255.248
 no ip split-horizon eigrp 90
 frame-relay map ip 10.2.0.2 102 broadcast
 frame-relay map ip 10.2.0.3 103 broadcast
!

router eigrp 90

network 10.2.0.1 0.0.0.0

no auto-summary

SPOKE1:
interface Serial0/0
 ip address 10.2.0.2 255.255.255.248
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 10.2.0.1 201 broadcast
 frame-relay map ip 10.2.0.3 201 broadcast
!
router eigrp 90 
network 10.2.0.2 0.0.0.0 
no auto-summary

SPOKE2:

interface Serial0/0
 ip address 10.2.0.3 255.255.255.248
 encapsulation frame-relay
 frame-relay map ip 10.2.0.1 301 broadcast
 frame-relay map ip 10.2.0.2 301 broadcast

!

router eigrp 90
 network 10.2.0.3 0.0.0.0
 network 10.3.0.2 0.0.0.0
 no auto-summary

EIGRP authentication

In EIGRP we can configure the authenticaton between the routers to form neighbours,EIGRP has a feature of "key chain" which we  can create number of keys and we can assign a time line for each of the key.This authentication can be done with a list of commands in global configuration mode.
"key chain name"
"key number"
"key-strings value"

after creating the keys we need to configure those on the which ever interface we want.From global configuration mode

"interface serial0/0"
"ip authentication mode eigrp asn md5"
"ip authentication key-chain eigrp asn name of the key chain"

if there is no time period for keys then the keys are valid for life time, if we want to configure the time period then we configure with commands
"accept-lifetime start  to end"
"send-lifetime start to end"

Note:The key number and key string should be always same on the routers to become neighbors.

Example:



considering "eigrp 90" and "network command"configured on the two routers, i configured the eigrp authentication on both routers

BB#
BB#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
BB(config)#key chain keys
BB(config-keychain)#key 1
BB(config-keychain-key)#key-string kumar
BB(config-keychain-key)#int s0/0
BB(config-if)#ip authentication mode eigrp 90 md5

*Mar  1 00:02:14.451: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 90: Neighbor 10.0.0.2 (Serial0/0) is down: authentication mode changed
BB(config-if)#ip authentication key-chain eigrp 90 keys
BB(config-if)#

LONDON#
LONDON#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
LONDON(config)#key chain keys
LONDON(config-keychain)#key 1
LONDON(config-keychain-key)#key-string kumar
LONDON(config-keychain-key)#int s0/0
LONDON(config-if)#ip authentication mode eigrp 90 md5

*Mar  1 00:06:46.963: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 90: Neighbor 10.0.0.1 (Serial0/0) is down: authentication mode changed
LONDON(config-if)#ip authentication key-chain eigrp 90 keys
LONDON(config-if)#

we check the key chain with using command "show key chain"

BB#sh key chain
Key-chain keys:
    key 1 -- text "kumar"
        accept lifetime (always valid) - (always valid) [valid now]
        send lifetime (always valid) - (always valid) [valid now]
BB#

as i didn't configure any life time the keys are always valid.



please post your valid comments.

Configuring /31 mask on a serial interfaces

Recently i came to know that, we can configure a /31 ip addressess on a point-to-point networks ,when i first learned this i wondered how the /31 is configured on p-to-p so i tried it on GNS3 and found a very interesting results, cisco added this feature in IOS 12.2 and later versions.

Point-to-point links only have two endpoints (hosts) and do not require broadcast support because any packet that is transmitted by one host is always received by the other host. Therefore the all-ones broadcast IP address is not required for a point-to-point interface.

The simplest way to explain RFC 3021 is to say that the use of a 31-bit prefix (created by applying a 31-bit subnet mask to an IP address) allows the all-zeros and all-ones IP addresses to be assigned as host addresses on point-to-point networks. Prior to RFC 3021 the longest prefix in common use on point-to-point links was 30-bits, which meant that the all-zeros and all-ones IP addresses were wasted.

The below table shows an example of the two IP addresses that are created when a 31-bit (otherwise known as 255.255.255.254 or /31) subnet mask is applied to the IP address 192.168.1.16.

  Two IP Addresses Created When a 31-Bit Subnet Mask (/31) Is Used 

Address	Description	Binary
192.168.1.16/31	First host address	11000000.10101000.00000001.00010000
192.168.1.17/31	Second host address	11000000.10101000.00000001.00010001

Based on the above explanation check this out

R1:




R2:




Reachability bet'n R1 and R2:

Configuring a Cisco Router as a Frame Relay Switch

Cisco router can be configured as a frame relay switch,in the above picture R1 acts as a frame-relay switch which i add the pvc's between R2 and R3,R2 and R4.Frames from a Frame Relay PVC arriving on an incoming interface are switched to a Frame Relay PVC on outgoing interface. During this process, the incoming DLCI in the arriving frames is replaced by an outgoing DLCI. Frame Relay switching is performed completely in Layer 2, and the Frame Relay switch pays no attention to Layer 3 information contained within the frames. The paths taken by the switched frames are completely based on the Frame Relay route table constructed.

Configuration:

R1#sh run
Building configuration...

Current configuration : 1144 bytes
!
version 12.3
!
hostname R1
!
frame-relay switching
!
!
!
!
interface Serial0/0
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clock rate 64000
 frame-relay intf-type dce
 frame-relay route 102 interface Serial0/1 201
 frame-relay route 103 interface Serial0/2 301
!
interface Serial0/1
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clock rate 64000
 frame-relay intf-type dce
 frame-relay route 201 interface Serial0/0 102
!
interface Serial0/2
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clock rate 64000
 frame-relay intf-type dce
 frame-relay route 301 interface Serial0/0 103
!
!
!
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
!
!
end

R2#sh run
Building configuration...
!
hostname R2
!
!
!
!
interface Serial0/0
 ip address 10.0.0.1 255.255.255.0
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 10.0.0.2 102
 frame-relay map ip 10.0.0.3 103
!
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
!
!
end


R4#sh run
Building configuration...

hostname R4
!
!
!
!
!
interface Serial0/1
 ip address 10.0.0.3 255.255.255.0
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 10.0.0.1 301
 frame-relay map ip 10.0.0.2 301
!
!
!
!
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
!
!
end






R3#sh run
Building configuration...

hostname R3
!
!
!
!
!
interface Serial0/0
 ip address 10.0.0.2 255.255.255.0
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 10.0.0.1 201
 frame-relay map ip 10.0.0.3 201
!
!

!
!
!
line con 0
 exec-timeout 0 0
 logging synchronous
line aux 0
line vty 0 4
!
!
end