IOS XR · PLATFORM

CDP and LLDP on IOS XR

XR1 (an NCS 5508) connects to R2 (an ISR 4451-X running IOS XE) and to XR3 (a Cisco 8808). IOS runs CDP by default, but IOS XR does not: CDP must be enabled globally and on each interface, and LLDP is off everywhere until you turn it on. Make every router see its neighbors in both protocols.

IOS XR track · IOS XR + Cisco IOS XE · 5 objectives

Open in simulator More IOS XR labs

Objectives

The simulator ticks each one as soon as the network meets it.

XR1: enable CDP globally and on Gi0/0/0/0 and Gi0/0/0/1, then commit.
XR3: enable CDP globally and on Gi0/0/0/0, then commit.
XR1 sees R2 and XR3 as CDP neighbors (show cdp neighbors).
Enable LLDP on all three routers: lldp on XR1 and XR3, lldp run on R2.
XR1 sees R2 and XR3 in LLDP, and R2 sees XR1 (show lldp neighbors).

Start this lab

Before you start

On IOS XR, "cdp" in global configuration only starts the process; each interface needs its own "cdp" line too. LLDP is the opposite: the global "lldp" command enables it on every interface, and an interface can stop transmitting or receiving with lldp → transmit disable / receive disable. A neighbor appears only when both ends run the protocol.

Concept

CDP and LLDP neighbor discovery on IOS XR

CDP (Cisco) and LLDP (IEEE 802.1AB) send a small advertisement out of each link: the device name, the port, the platform and the software version. The neighbor stores it for the hold time, so show cdp neighbors or show lldp neighbors tells you what is cabled to each port. IOS runs CDP by default; IOS XR runs neither protocol until you configure it.