Friday, July 21, 2017

EIGRP - summarization - part 1

Today I would like to play with EIGRP, check its recommended designs, settings, etc. Below you can see a diagram:




I have a standard configuration (named version) on all of them:

router eigrp TEST1
 !
 address-family ipv4 unicast autonomous-system 100
 !
 topology base
 exit-af-topology
 network 10.1.0.0 0.0.0.255
 network 10.0.0.0 0.0.0.255
 
There are three topics I plan to go through in this and 2 next posts:
1) link failures without summarization
2) link failures with summarization
3) link failures with an EIGRP stub routing feature
Let's start from the basic principals and then we move on.
In stable network we should see 'hello' packets sent every 5 seconds:



R1#debug eigrp packets all
 (UPDATE, REQUEST, QUERY, REPLY, HELLO, UNKNOWN, PROBE, ACK, STUB, SIAQUERY, SIAREPLY)
EIGRP Packet debugging is on
R1#
*Jul 20 22:54:20.426: EIGRP: Sending HELLO on Fa0/0 - paklen 20
*Jul 20 22:54:20.426: AS 100, Flags 0x0:(NULL), Seq 0/0 interfaceQ 0/0 iidbQ un/rely 0/0
*Jul 20 22:54:20.466: EIGRP: Received HELLO on Fa1/0 - paklen 20 nbr 10.1.0.6
*Jul 20 22:54:20.466: AS 100, Flags 0x0:(NULL), Seq 0/0 interfaceQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
*Jul 20 22:54:21.134: EIGRP: Received HELLO on Fa0/0 - paklen 20 nbr 10.0.0.3
*Jul 20 22:54:21.134: AS 100, Flags 0x0:(NULL), Seq 0/0 interfaceQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
R1#
*Jul 20 22:54:22.286: EIGRP: Sending HELLO on Fa1/0 - paklen 20
*Jul 20 22:54:22.286: AS 100, Flags 0x0:(NULL), Seq 0/0 interfaceQ 0/0 iidbQ un/rely 0/0
R1#
*Jul 20 22:54:23.558: EIGRP: Received HELLO on Fa0/0 - paklen 20 nbr 10.0.0.2
*Jul 20 22:54:23.558: AS 100, Flags 0x0:(NULL), Seq 0/0 interfaceQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
R1#no
*Jul 20 22:54:24.846: EIGRP: Sending HELLO on Fa0/0 - paklen 20
*Jul 20 22:54:24.846: AS 100, Flags 0x0:(NULL), Seq 0/0 interfaceQ 0/0 iidbQ un/rely 0/0
*Jul 20 22:54:25.358: EIGRP: Received HELLO on Fa1/0 - paklen 20 nbr 10.1.0.6
*Jul 20 22:54:25.358: AS 100, Flags 0x0:(NULL), Seq 0/0 interfaceQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
R1#
 
The hellos are sent to multicast address 224.0.0.10:



Hello packet doesn't contain too much information but there are some important values which are needed to establish neighborship:
 
 
 
K- values have to match on all routers and by default K1 and K3 are enabled. They are: bandwidth and delay, respectively. Let's see what happens when we change one value on R1:


 On R1 K1 value is 0:

R1#sh run | s eigrp
router eigrp TEST1
!
address-family ipv4 unicast autonomous-system 100
!
topology base
exit-af-topology
network 10.0.0.0 0.0.0.255
network 10.1.0.0 0.0.0.255
metric weights 0 0 0 1 0 0 0
exit-address-family
R1#


 
 
Link Failures without summarization.

Without any summarization the routing table has 21 entries:

R2#sh ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
 D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
 N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
 E1 - OSPF external type 1, E2 - OSPF external type 2
 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
 ia - IS-IS inter area, * - candidate default, U - per-user static route
 o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
 + - replicated route, % - next hop override

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 21 subnets, 2 masks
C 10.0.0.0/24 is directly connected, FastEthernet0/0
L 10.0.0.2/32 is directly connected, FastEthernet0/0
D 10.1.0.0/24 [90/153600] via 10.0.0.1, 00:00:13, FastEthernet0/0
D 10.1.1.0/24 [90/154240] via 10.0.0.1, 00:00:12, FastEthernet0/0
D 10.1.2.0/24 [90/154240] via 10.0.0.1, 00:00:12, FastEthernet0/0
D 10.1.3.0/24 [90/154240] via 10.0.0.1, 00:00:12, FastEthernet0/0
D 10.1.4.0/24 [90/154240] via 10.0.0.1, 00:00:12, FastEthernet0/0
D 10.1.5.0/24 [90/154240] via 10.0.0.1, 00:00:12, FastEthernet0/0
C 10.2.0.0/24 is directly connected, FastEthernet1/0
L 10.2.0.2/32 is directly connected, FastEthernet1/0
D 10.2.1.0/24 [90/103040] via 10.2.0.4, 00:00:40, FastEthernet1/0
D 10.2.2.0/24 [90/103040] via 10.2.0.4, 00:00:40, FastEthernet1/0
D 10.2.3.0/24 [90/103040] via 10.2.0.4, 00:00:40, FastEthernet1/0
D 10.2.4.0/24 [90/103040] via 10.2.0.4, 00:00:40, FastEthernet1/0
D 10.2.5.0/24 [90/103040] via 10.2.0.4, 00:00:40, FastEthernet1/0
D 10.3.0.0/24 [90/153600] via 10.0.0.3, 00:29:54, FastEthernet0/0
D 10.3.1.0/24 [90/154240] via 10.0.0.3, 00:29:54, FastEthernet0/0
D 10.3.2.0/24 [90/154240] via 10.0.0.3, 00:29:54, FastEthernet0/0
D 10.3.3.0/24 [90/154240] via 10.0.0.3, 00:29:54, FastEthernet0/0
D 10.3.4.0/24 [90/154240] via 10.0.0.3, 00:29:54, FastEthernet0/0
D 10.3.5.0/24 [90/154240] via 10.0.0.3, 00:29:54, FastEthernet0/0
R2#


I shutdown an interface Loop5 on R3 to see how EIGRP deals with missing access to 10.3.5.0/24 network.

*Jul 21 14:04:07.287: EIGRP: Received UPDATE on Fa0/0 - paklen 44 nbr 10.2.0.2
*Jul 21 14:04:07.287: AS 100, Flags 0x0:(NULL), Seq 227/35 interfaceQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
*Jul 21 14:04:07.291: {type = 602, length = 44}
*Jul 21 14:04:07.295: {vector = {afi = 1, tid = 0}
*Jul 21 14:04:07.295: {routerid = 10.3.5.5
*Jul 21 14:04:07.299: {offset = 0, priority = 0, reliability = 255, load = 1,
*Jul 21 14:04:07.299: mt
R4#u = {1500:[00, 05, DC]), hopcount = 2,
*Jul 21 14:04:07.299: delay = 281474976710655, bw = 100000,
*Jul 21 14:04:07.303: reserved = 00, opaque_flags = 00}
*Jul 21 14:04:07.303: {nh:00000000}
*Jul 21 14:04:07.307: {180A0305}
*Jul 21 14:04:07.311: }
*Jul 21 14:04:07.311: EIGRP: Enqueueing ACK on Fa0/0 - paklen 0 nbr 10.2.0.2 tid 0
*Jul 21 14:04:07.311: Ack seq 227 iidbQ un/rely 0/0 peerQ un/rely 1/0 route: 10.3.5.0/24
*Jul 21 14:04:07.319: EIGRP: Sending ACK on Fa0/0 - paklen 0 nbr 10.2.0.2 tid 0
*Jul 21 14:04:07.319: AS 100, Flags 0x0:(NULL), Seq 0/227 interfaceQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 1/0
*Jul 21 14:04:07.323: EIGRP: Enqueueing QUERY on Fa0/0 - paklen 0 tid 0 iidbQ un/rely 0/1 serno 129-129
*Jul 21 14:04:07.327: EIGRP: Sending QUERY on Fa0/0 - paklen 44 tid 0
*Jul 21 14:04:07.327: AS 100, Flags 0x0:(NULL), Seq 38/0 interfaceQ 0/0 iidbQ un/rely 0/0 serno 129-129
*Jul 21 14:04:07.327: {type = 602, len
R4#gth = 44}
*Jul 21 14:04:07.327: {vector = {afi = 1, tid = 0}
*Jul 21 14:04:07.327: {routerid = 10.3.5.5
*Jul 21 14:04:07.327: {offset = 0, priority = 0, reliability = 255, load = 1,
*Jul 21 14:04:07.327: mtu = {1500:[00, 05, DC]), hopcount = 2,
*Jul 21 14:04:07.327: delay = 281474976710655, bw = 100000,
*Jul 21 14:04:07.327: reserved = 00, opaque_flags = 04}
*Jul 21 14:04:07.327: {nh:00000000}
*Jul 21 14:04:07.327: {180A0305}
*Jul 21 14:04:07.327: }
*Jul 21 14:04:07.339: EIGRP: Received ACK on Fa0/0 - paklen 0 nbr 10.2.0.2
*Jul 21 14:04:07.339: AS 100, Flags 0x0:(NULL), Seq 0/38 interfaceQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/1
*Jul 21 14:04:07.339: EIGRP: FastEthernet0/0 multicast flow blocking cleared
*Jul 21 14:04:07.379: EIGRP: Received REPLY on Fa0/0 - paklen 44 nbr 10.2.0.2
*Jul 21 14:04:07.379: AS 100, Flags 0x0:(NULL), Seq 229/38 interfaceQ 0/0 iidbQ un/rely 0/0 peerQ
R4# un/rely 0/0
*Jul 21 14:04:07.383: {type = 602, length = 44}
*Jul 21 14:04:07.383: {vector = {afi = 1, tid = 0}
*Jul 21 14:04:07.383: {routerid = 10.3.5.5
*Jul 21 14:04:07.383: {offset = 0, priority = 0, reliability = 255, load = 1,
*Jul 21 14:04:07.383: mtu = {1500:[00, 05, DC]), hopcount = 2,
*Jul 21 14:04:07.383: delay = 281474976710655, bw = 100000,
*Jul 21 14:04:07.383: reserved = 00, opaque_flags = 00}
*Jul 21 14:04:07.383: {nh:00000000}
*Jul 21 14:04:07.383: {180A0305}
*Jul 21 14:04:07.383: }


As you can see R4 received update that network 10.3.5.0/24 is not accessible and then R4 sent query asking R2 about any alternative path to this network. In queries and replies there is a delay value = 281474976710655, what is interpreted by wireshark as ‘infinity’:





 
 
As you can see the network is pretty noisy. Now if any network is down behind R5, all devices receive update about it, despite there is no backup path. With more devices and bigger routing tables the number of updates would be huge. We can fix it by enabling summarization to limit number of information exchanged between routers. I will continue the topic in the next post.

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