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nx.os.and.cisco.nexus.switching.2nd.edition.1587143046

Nexus Switching 2nd Edition

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called the Diffusing Update Algorithm (DUAL). The primary advantage that DUAL provides<br />

over other routing algorithms is the capability to provide loop-free topologies at every stage<br />

of network convergence. When joined with the other capabilities of EIGRP, such as its<br />

multiprotocol nature, WAN-friendly neighboring <strong>and</strong> updating capabilities, <strong>and</strong> flexible<br />

summarization <strong>and</strong> quick convergence, it makes a powerful routing protocol.<br />

EIGRP forms adjacencies with its directly connected neighbors to exchange routing updates<br />

similar to a link state protocol. During the initial neighbor formation, attributes such as<br />

smooth round-trip time (SRTT), hold time, retry timeout, IP address, <strong>and</strong> interface on which<br />

the hello was received are negotiated <strong>and</strong> recorded in a neighbor table, as demonstrated in<br />

Example 3-1.<br />

Example 3-1. EIGRP Neighbors<br />

Click here to view code image<br />

Congo# show ip eigrp ne<br />

IP-EIGRP neighbors for process 100 VRF default<br />

H Address Interface Hold Uptime SRT<br />

(sec)<br />

(ms<br />

Num<br />

1 10.10.10.3 Vlan10 11 01:42:49 44<br />

0 192.168.1.38 Eth1/18 14 01:52:06 41<br />

The hell<strong>os</strong> between the EIGRP neighbors are the mechanism for maintaining the adjacency.<br />

Within the hello is a hold timer that tells EIGRP the maximum time before the next hello<br />

should be received. By default, the hold timer is three times the hello interval. If the hold<br />

timer is exceeded before another hello is received, EIGRP considers the neighbor<br />

unreachable <strong>and</strong> informs DUAL. The network’s topology is recalculated <strong>and</strong> bounded,<br />

partial updates are sent to the remaining neighbors, <strong>and</strong> the network begins to converge.<br />

Configuring EIGRP<br />

EIGRP within NX-OS is compatible with EIGRP on IOS devices enabling a smooth<br />

integration of Nexus equipment with existing gear. Configuring EIGRP within NX-OS will<br />

be similar yet distinctly different in some aspects to traditional IOS configuration. These<br />

differences will be highlighted throughout the section.<br />

Enabling EIGRP is a multistep process that will be covered in detail. The following is a<br />

quick listing of steps to enable a basic configuration of EIGRP:<br />

1. Enable EIGRP.<br />

2. Configure the EIGRP routing process with support for IPv4 or IPv6.<br />

3. Assign interfaces to the instance tag.<br />

4. Configure passive interfaces if necessary.<br />

5. Configure network summarization.

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