# After adding a new switch, the host connected to the new switch do not ping with the hosts in the original topology

**URL:** <https://forum.p4.org/t/after-adding-a-new-switch-the-host-connected-to-the-new-switch-do-not-ping-with-the-hosts-in-the-original-topology/1239>\
**Category:** Getting Started with P4\
**Created:** [December 28, 2024, 3:01am UTC](https://forum.p4.org/t/after-adding-a-new-switch-the-host-connected-to-the-new-switch-do-not-ping-with-the-hosts-in-the-original-topology/1239 "2024-12-28T03:01:11Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![dongcheng1218](https://avatars.discourse-cdn.com/v4/letter/d/e47c2d/32.png) [@dongcheng1218](https://forum.p4.org/u/dongcheng1218)\
**Post date:** [December 28, 2024, 3:01am UTC](https://forum.p4.org/t/after-adding-a-new-switch-the-host-connected-to-the-new-switch-do-not-ping-with-the-hosts-in-the-original-topology/1239/1 "2024-12-28T03:01:11Z")

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Hi, while studying the opennetworkinglab/ngsdn-tutorial project, I want to expand the topology by adding a new switch, leaf3, and a new host, h3, and there is a problem that h3 pinging h2 can ping through, but h2 pinging h3 can’t ping through.

 ![屏幕截图 2024-12-28 110019](https://us1.discourse-cdn.com/flex019/uploads/p4/original/1X/6f62f00500f84799a2f91ab7304b3aa880151f48.jpeg)

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**Author:** ![andyfingerhut](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.p4.org/andyfingerhut/32/17_2.png) [@andyfingerhut](https://forum.p4.org/u/andyfingerhut)\
**Post date:** [December 28, 2024, 5:14am UTC](https://forum.p4.org/t/after-adding-a-new-switch-the-host-connected-to-the-new-switch-do-not-ping-with-the-hosts-in-the-original-topology/1239/2 "2024-12-28T05:14:24Z")

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Unfortunately, I have not used that particular P4 setup before, so I do not have specific advice on exactly what you might be missing. Someone else may read your question and be able to give that kind of advice.

I do, however, have general advice on troubleshooting these kinds of problems, which I have written about here: [The host ping across switches is unreachable - #4 by andyfingerhut](https://forum.p4.org/t/the-host-ping-across-switches-is-unreachable/1228/4)