Troubleshooting - using Telnet to test transport layer ports


When SSH sessions into a Cisco IOS device fail, there are several ways to troubleshoot them including:

- `debug ip ssh` - this command will enable the SSH debugging on the switch to which you wish to connect.
- Client side debugging - When using Putty, enable logging by going to **Logging** and select **SSH Packets** before connecting. When using OpenSSH, run it with the **-v** flag.


SSH connectivity - troubleshooting

Routing - default gateway

Routing - default routing using DHCP

Routing - directed broadcast

Routing - fully specified route

Routing - ip default-network command

Routing - l2transport

Routing - link-local IPv6 next hop address needs exit interface

Routing - network vs redistribute connected commands

Routing - redistribute command

Routing - redistribution and the routing table

Routing - route tagging

Routing - seed metrics

Routing - what is a WAN port

Routing - what is recursive routing

Routing - what is redistribution

Routing NX-OS passive-interface default

Routing Table

Routing in both directions

Routing what if the administrative distance is the same

Routing

SD-WAN - EVE-NG connection options

SD-WAN - Unique Site IDs for vEdges

SD-WAN - cEdge

SD-WAN - vAnalytics

SD-WAN - vBond

SD-WAN - vEdge full mesh

SD-WAN - vEdge vs cEdge

SD-WAN - vEdge

SD-WAN - vManage

SD-WAN - vSmart

SD-WAN OMP VPN Route Status Codes

SD-WAN Template Attach Error on vManage

SD-WAN set TLOC color

SD-WAN

SDN - what is orchestration

SG300-10 - InterVLAN routing defaults

SNMP - Engine ID

SNMP - Index shuffling

SNMP - Simple Network Management Protocol

SNMP - Version 3 security levels

SNMP - snmp-server community and host commands

SNMP monitoring routing on a Nexus device

SNMP trap vs inform

SNMP walk

SPAN capturing control packets

SPAN multiple destination ports on Cisco IOS device

SPAN using VLANs as a source on a Nexus device

SPAN

SSH - domain-name prerequisite

SSM Multicast Group Verification

STP - Aging time reduction with a TCN

STP - Aging time return to default

STP - BPDU Filter Use Cases

STP - BPDU generation and port roles

STP - BPDUGuard, BPDUFilter, and Portfast

STP - BPDUs on a switch where STP is disabled

STP - BPDUs, VLAN IDs, and PVST+

STP - Cost of last link added by receiving switch

STP - Disabling spanning-tree

STP - Dispute

STP - Factors to Consider When Choosing a Root Bridge

STP - Learning State

STP - MST CIST Root

STP - MST CST and CIST

STP - MST Virtual Bridge and its role in interfacing with other STP topologies

STP - MST and PVST+ selecting root port

STP - MST maps groups of VLANs

STP - MST region attributes

STP - MST viewed as a single switch by PVST+

STP - Max Age vs Message Age

STP - Multiple Spanning Tree (MST)

STP - Multiple types of STP on the same switch

STP - PVST+ and Rapid PVST+ interaction

STP - Per VLAN Spanning Tree plus (PVST+)

STP - RSTP BPDU Flags and their usage

STP - RSTP EdgePort

STP - RSTP Proposal Timer Operation

STP - RSTP convergence process

STP - RSTP port roles

STP - RSTP prerequisites for immediate move to forward state

STP - RSTP proposal-agreement process

STP - RSTP while timer cannot be observed

STP - RSTP while timer

STP - Root Inconsistency State

STP - Root Link Query (RLQ) BPDU

STP - Shortest Path Bridging (SPB)

STP - Time to select root bridge

STP - Topology Change Acknowledgement (TCA)

STP - UDLD and Fiber Links

STP - Understanding MST regional root identifier and proposal-agreement process

STP - UplinkFast and reconvergence

STP - UplinkFast and root port delay timer

STP - UplinkFast

STP - bridge priority

STP - connecting one port to another port on the same switch

STP - determining the blocked port using port ID

STP - port identification

STP - port roles

SSH connectivity - troubleshooting

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