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DHCP issue on C9800-40

zexinfinite
Level 1
Level 1

Hi folks,

 

I noticed some of wireless client faced DHCP renew issue when I using C9500-48Y-4C as DHCP server, and C9800-40 as wireless controller (Access point is using local mode).

During DHCP renew, the wireless client will send the DHCP request packet to DHCP server, but the devices may not received response from DHCP server after it send out several DHCP request, then it will send DHCP discover again and waiting for the IP assignment (At the moment, the wireless client will assigned IP with 169.X.X.X).

I captured the packet on both wireless client and core switch, and I noticed wireless client only send out 1 packet for each type of DHCP packet, but the packet duplicated after it passthrough C9800-40, and I'm afraid it may triggered CoPP if there have so many DHCP request or DHCP discover packet arrived core switch at the same time.

 

Does anyone faced this issue before?

 

=================
On laptop
=================

1 2021-10-26 02:30:33.896986 192.168.54.64 192.168.48.1 DHCP 67 342 DHCP Release - Transaction ID 0xe6385c6
2 2021-10-26 02:30:37.094294 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
3 2021-10-26 02:30:39.098121 192.168.48.1 192.168.54.64 DHCP 68 363 DHCP Offer - Transaction ID 0x22197da8
4 2021-10-26 02:30:39.100442 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
5 2021-10-26 02:30:39.104040 192.168.48.1 192.168.54.64 DHCP 68 363 DHCP ACK - Transaction ID 0x22197da8

=================
On core switch
=================

1 2021-10-26 02:30:34.466944 192.168.54.64 192.168.48.1 DHCP 67 342 DHCP Release - Transaction ID 0xe6385c6
2 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
3 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
4 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
5 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
6 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
7 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
8 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
9 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
10 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
11 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
12 2021-10-26 02:30:37.663074 0.0.0.0 255.255.255.255 DHCP 67 342 DHCP Discover - Transaction ID 0x22197da8
13 2021-10-26 02:30:39.663932 192.168.48.1 192.168.54.64 DHCP 68 363 DHCP Offer - Transaction ID 0x22197da8
14 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
15 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
16 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
17 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
18 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
19 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
20 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
21 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
22 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
23 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
24 2021-10-26 02:30:39.669042 0.0.0.0 255.255.255.255 DHCP 67 378 DHCP Request - Transaction ID 0x22197da8
25 2021-10-26 02:30:39.669736 192.168.48.1 192.168.54.64 DHCP 68 363 DHCP ACK - Transaction ID 0x22197da8

2 Replies 2

Scott Fella
Hall of Fame
Hall of Fame

Out of curiosity, do you see this issue on wired devices too?  

-Scott
*** Please rate helpful posts ***

JPavonM
VIP
VIP

Which code release are you running in c9800? Which AP model is affected?

I've experienced some similar issues and at the end I was hitting CSCvw30043 that is fixed in 17.3.3.

The workaround was to bounce the radio interface which is affected.

HTH
-Jesus
*** Please rate helpful responses ***

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