Categories
CCNP (Pre 2020) CCNP Enterprise Core (350-401) Services

First Hop Redundancy Protocols

First Hop Redundancy Protocols are the Layer 3 answer to resiliency. It adds multiple Layer 3 paths to allow devices to reach their destinations.

First Hop Redundancy Protocols by creating a virtual gateway for the network that is shared between Layer 3 devices. There are many different protocols but three are relevant for the CCNP exam:

  • Hot Standby Router Protocol (HSRP)
  • Virtual Router Redundancy Protocol (VRRP)
  • Gateway Load Balancing Protocol (GLBP)
Categories
CCNP (Pre 2020) CCNP Enterprise Core (350-401) Cisco Datalink Layer

UDLD – Unidirectional Link Detection

Unidirectional Link Detection allows for monitoring of physical media that separates its send and receive media, like fibre optic cables.

UDLD operates by transmitting a packet to the neighbour device that contains a system and port ID of the originating interface. The receiving interface gets this information and mirrors it back including its own system and port ID. This process continues to ensure that both send and receive parts of the link have communication between them.

Unidirectional Link Detection has two operating modes, normal and aggressive.

  • Aggressive mode sends eight additional packets in one second intervals when a UDLD packet is not acknowledged by the neighbouring switch. If none of those packets are acknowledged the port is changed into a error disabled state.
  • Normal mode does not send additional packets or disable the interface when a packet is not acknowledged. It changes the link status to undetermined and the port continues to be utilised regardless of what fault state it is in.

Unidirectional Link Detection can be enabled globally with the command udld enable with the optional additional suffix keyword of aggressive to enable aggressive mode. Enabling UDLD globally will switch on the UDLD mechanisms on all SFP ports.

Individual ports can have UDLD capabilities disabled in interface configuration mode with the command udld port disable

In order for UDLD to function correctly, both ends of the switch must have UDLD enabled to communicate packets correctly. The status of UDLD can be checked with the command show udld neighbors

Categories
CCNP (Pre 2020) TSHOOT

TSHOOT Topology

The new TSHOOT exam requires you to isolate issues on a defined network topology. The purpose of the exam is to evaluate troubleshooting skills, not how quickly you can grasp a network topology you have never seen. To this end, it is Cisco’s intent that the exam network topology be available for review before the candidate attempt the exam.

https://learningnetwork.cisco.com/thread/10965

As practice I mirrored the topology in the linked thread to an easy to read topology below.

A - VLAN 10 - 10.2.1.0/24DSW1 - 10.2.1.1DSW2 - 10.2.1.2
B - VLAN 20 - 10.2.2.0/24
DSW1 - 10.2.2.2
DSW2 - 10.2.2.1
C - DSW1 <-> R4 - 10.1.4.4/30
DSW1 - 10.1.4.6
R4 - 10.1.4.5
D - DSW2 <-> R4 - 10.1.4.8/30
DSW2 - 10.1.4.10 
R4 - 10.1.4.9
E - R4 <-> R3 - 10.1.1.8/30
R4 - 10.1.1.10
R3 - 10.1.1.9
F - R3 <-> R2 - 10.1.1.4/30
R3 - 10.1.1.6
R2 - 10.1.1.5
G - R2 <-> R1 - 10.1.1.0/30
R2 - 10.1.1.2
R1 - 10.1.1.1
H - R1 <-> WAN - 209.65.200.224/30
R1 - 209.65.200.225
ISP Router - 209.65.200.226
X - Link between DSW1 and DSW2 (not shown) - 10.2.4.12/30
DSW1 - 10.2.4.13
DSW2 - 10.2.4.14