---
name: transit-gateway-verifying-connectivity
title: How do I verify and deal with connectivity issues on my transit gateways?
description: Several issues exist that can cause problems when attempting to communicate between resources that are connected to your IBM Cloud® Transit Gateway.
last-updated: 2023-02-23
---

> ## Documentation Index
> The table of contents for this documentation set is at https://cloud.ibm.com/docs/transit-gateway?format=markdown
> The index for all IBM Cloud docs is at: https://cloud.ibm.com/docs/llms.txt
> Use these files to discover more information as needed.

# How do I verify and deal with connectivity issues on my transit gateways?
{: #troubleshooting-connectivity}

Several issues exist that can cause problems when attempting to communicate between resources that are connected to your IBM Cloud® Transit Gateway.
{: shortdesc}

You might receive error messages that state that you need to check whether the resource that you are requesting to access exists, and to review your network topology.
{: tsSymptoms}

Known issues include incorrect permissions, overlapping VPC prefixes and classic infrastructure subnets, networking interface card routing, access control lists, firewalls and gateway appliances, and routing in classic virtual server instances.
{: tsCauses}

To fix the connectivity issues you're encountering, review the following information topics:
{: tsResolve}

* [Connectivity issue basics](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-connectivity-basics&format=markdown)
* [Working with firewalls and gateway appliances](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-firewalls-gateways&format=markdown)
* [Dealing with overlapping VPC prefixes and classic infrastructure subnets](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-overlapping-vpc-prefixes-and-classic-subnets&format=markdown)
* [Working with Network Interface Card Routing](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-tg-nic&format=markdown)
* [Routing in classic virtual server instances](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-routing-classic-vsi&format=markdown)
* [GRE tunnel connectivity issues](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-gre-tunnel-conn-issues&format=markdown)