Tag Archives: 3.5a

3.5 EIGRP [for IPv4 and IPv6]

eigrp neighbor table

 

the H column records the order in which the neighbors were learned

address and interface columns record the ip address of the neighbor and the interface on which the neighbor’s Hello’s are received

the Hold time is the amount of time that a router will consider a neighbor alive without receiving  hello packets. The hold time is typically three times the hello interval. You can adjust the hold time with the ip hold-time eigrp command.

uptime the time since the neighbor was added to the table

SRTT (Smoothed Round-Trip Time) With EIGRP, a purposefully slowly changing measurement
of round-trip time between neighbors, from which the EIGRP RTO is calculated.

RTO (Retransmission Timeout) With EIGRP, a timer starts when a reliable (to be
acknowledged) message is transmitted. For any neighbor(s) failing to respond in its RTO, the
RTP protocol causes retransmission. RTO is calculated based on SRTT.

Q cnt(count) indicates the number of enqueued packets

Seq Num is the sequence number of the last update, query, or reply packet received from the neighbor

 

3.5.a Describe packet types

3.5.a [i] Packet types [hello, query, update, and such]

EIGRP uses five packet types:

● Hello/ Acks

● Updates

● Queries

● Replies

● Requests

Hellos are multicast for neighbor discovery/ recovery. They do not require acknowledgment. A hello with no data is also used as an acknowledgment (Ack). Acks are always sent using a unicast address and contain a non-zero acknowledgment number.

Updates are used to convey reachability of destinations . When a new neighbor is discovered, update packets are sent so the neighbor can build up its topology table. In this case, update packets are unicast. In other cases, such as a link cost change, updates are multicast. Updates are always transmitted reliably.

Queries and replies are sent when destinations go into Active state. Queries are always multicast unless they are sent in response to a received query. In this case, it is unicast back to the successor that originated the query. Replies are always sent in response to queries to indicate to the originator that it does not need to go into Active state because it has feasible successors. Replies are unicast to the originator of the query. Both queries and replies are transmitted reliably.

Request packets are used to get specific information from one or more neighbors. Request packets are used in route server applications. They can be multicast or unicast. Requests are transmitted unreliably.

The sequence TLV contains a list of the nodes that should not listen to multicast packets while the recovery takes place. While recovering, each reliable multicast packet transmitted has the CR (conditional receive) bit set to indicate that it should be processed only if the receiving node’s was not present in the preceding sequence TLV packet.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Location 3034).  . Kindle Edition.

http://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/13669-1.html#packet_formats

 

3.5 EIGRP [for IPv4 and IPv6]

3.5.a Describe packet types

3.5.a [i] Packet types [hello, query, update, and such]

EIGRP Packet Types:

Hello: used to establish neighborship

Update: used to update routing information

Query: used to ask for routing information

Reply: used to reply to queries

Ack: acknowledges reliable packets

Note: Update, Query and Reply require Ack’s

EIGRP uses the mulitcast address 224.0.0.10 for the exchange of hello’s, and the AS numbers must match. On broadcast, multipoint, point-to-point serial and point-to-point subinterface links greater than T1 speed, Hellos are sent every 5 seconds. For slower links hellos are sent every 60 seconds. The hold-time is three times the hello value. Unlike OSPF, these setting do not have to match.

Update, query and reply packets require acknowledgement, whereas hello and ack do not require ack.

Neighborship reset occurs after a 16 retry limit is reached. Slow neighbors will be sent unicast updates instead.

3.5 EIGRP [for IPv4 and IPv6]

sh ip eigrp interfaces detail…

kind of a funky command, but it shows the hello time (default is 5, of course)…

r3(config-if)#do sh ip eigrp int det
IP-EIGRP interfaces for process 100

Xmit Queue   Mean   Pacing Time   Multicast    Pending
Interface        Peers  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes
Fa0/0              2        0/0        19       0/1           80           0
Hello interval is 5 sec
Next xmit serial <none>
Un/reliable mcasts: 0/14  Un/reliable ucasts: 23/11
Mcast exceptions: 5  CR packets: 4  ACKs suppressed: 4
Retransmissions sent: 4  Out-of-sequence rcvd: 0
Authentication mode is not set

r3(config-if)#ip hello-interval eigrp 100 10
r3(config-if)#do sh ip eigrp int det
IP-EIGRP interfaces for process 100

Xmit Queue   Mean   Pacing Time   Multicast    Pending
Interface        Peers  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes
Fa0/0              2        0/0        19       0/1           80           0
Hello interval is 10 sec
Next xmit serial <none>
Un/reliable mcasts: 0/14  Un/reliable ucasts: 23/11
Mcast exceptions: 5  CR packets: 4  ACKs suppressed: 4
Retransmissions sent: 4  Out-of-sequence rcvd: 0
Authentication mode is not set

3.5.a Describe packet types

i didn’t catch this on my last reading… note also that doyle sets hello/ack as distinct packet types whereas cisco pairs them as below…

from doyle:

Requests were a type of packet originally intended for use in route servers. This
application was never implemented, and request packets are noted here only because
they are mentioned in some older EIGRP documentation.

from cisco: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f07.shtml

Packet Formats

EIGRP uses five packet types:

  • Hello/Acks
  • Updates
  • Queries
  • Replies
  • Requests

Request packets are used to get specific information from one or more neighbors. Request packets are used in route server applications. They can be multicast or unicast. Requests are transmitted unreliably.

and wendell below from ccie r&s:

Hello Identifies neighbors, exchanges parameters, and is sent periodically as a
keepalive function
Update Informs neighbors about routing information
Ack Acknowledges Update, Query, and Response packets
Query Asks neighboring routers to verify their route to a particular subnet
Reply Sent by neighbors to reply to a Query
Goodbye Used by a router to notify its neighbors when the router is gracefully shutting down

note: wendell separates hello/ack, doesn’t mention request, sia-query, sia-reply and includes goodbye…

and wireshark chimes in:

eigrp_cap