Re: Router Not Getting DHCP - Keep in Requesting & Purging Sta

Muhd · ‎10-07-2024

Hi,

My router not getting DHCP IP from ISP router. This issue sometime happen at my branch office. The only workaround I can do right now is shutdown the interface for 3 to 4 hours & after no shut the router able to get the IP. During the problem i check the DHCP status keep in requesting & purging state. Anyone can assist me on this / have encoutering this issues ?

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Kuantan-VG# sh dhcp lease
Temp IP addr: 10.150.12.165 for peer on Interface: GigabitEthernet0/0/1
Temp sub net mask: 255.255.128.0
DHCP Lease server: 10.150.127.254, state: 4 Requesting
DHCP transaction id: F96E0C2D
Lease: 10800 secs, Renewal: 0 secs, Rebind: 0 secs
Next timer fires after: 00:00:01
Retry count: 4 Client-ID: cisco-4ce1.757b.5de1-Gi0/0/1
Client-ID hex dump: 636973636F2D346365312E373537622E
356465312D4769302F302F31
Hostname: Kuantan-VG
Kuantan-VG#
Kuantan-VG# sh dhcp lease
Temp IP addr: 10.150.12.165 for peer on Interface: GigabitEthernet0/0/1
Temp sub net mask: 255.255.128.0
DHCP Lease server: 10.150.127.254, state: 11 Purging
DHCP transaction id: F96E0C2D
Lease: 10800 secs, Renewal: 0 secs, Rebind: 0 secs
Next timer fires after: 00:00:31
Retry count: 0 Client-ID: cisco-4ce1.757b.5de1-Gi0/0/1
Client-ID hex dump: 636973636F2D346365312E373537622E
356465312D4769302F302F31
Hostname: Kuantan-VG
Kuantan-VG#

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For Debug I only found this :

Oct 7 15:39:10.748: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:39:10.749: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:39:10.750: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:39:40.771: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:39:40.772: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:39:40.773: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:40:04.948: DHCPD: checking for expired leases.
Oct 7 15:40:15.803: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:40:15.805: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:40:15.806: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:40:55.830: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:40:55.831: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:40:55.832: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:41:36.518: %SYS-5-CONFIG_I: Configured from console by admin on vty0 (192.168.13.87)
Oct 7 15:41:40.853: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:41:40.854: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:41:40.855: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:42:04.948: DHCPD: checking for expired leases.
Oct 7 15:42:30.873: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:42:30.874: DHCPD: IP address change on interface GigabitEthernet0/0/1
Oct 7 15:42:30.875: DHCPD: IP address change on interface GigabitEthernet0/0/1
Kuantan-VG#

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Interface Configuration :

!
interface GigabitEthernet0/0/1
description CUBE to SIP Trunk
ip address dhcp
media-type rj45
negotiation auto
!

Anyone can assist me. TQ

MHM Cisco World · ‎10-07-2024

sorry I dont get issue here
your WAN is not get IP from DHCP ?

if Yes then I think we need to see
debug ip dhcp <<- share this

also do you see any flapping in link ?

MHM

Muhd · ‎10-07-2024

Yah, the int Gig 0/0/1 facing the ISP not getting IP Address. Let me run some debug and share to you later.

No flapping detected in the link. Btw, Thanks for the reply.

MHM Cisco World · ‎10-07-2024

Take your time

MHM

Muhd · ‎10-07-2024

Hi,

Just collect some debug & also i attached show run and show ip int in the notepad, but now the router able to get the IP from ISP after I shutdown & no shut for around 5 hours. I think the debug output may not help since the now the router able to getting IP Address from ISP.

MHM Cisco World · ‎10-07-2024

Thanks friend but this don't what I want

There are

Debug ip dhcp <<- this if R behave like client

Debug ip dhcp server <<-this if R behave like server

So I need to see when R behave like client

MHM

Muhd · ‎10-07-2024

Hi, I getting invalid command when run debug ip dhcp, btw for now the issue was solve, in future i believe it will happen again. This issue happen quiet some time at several branch office. I will keep you posted & thanks for the support.

@Flavio Miranda previously I already open case with my ISP & they inform their configuration was fine.

Muhd · ‎10-10-2024

Hi,

Today I faced another DHCP issues.

I attahced the debug and show run for your reference.

for debug i run : debug dhcp snooping event, debug dhcp snooping packet & debug dhcp detail

-----------------------------------------------------

below the is the status. the status keep purging

KB-VG#show dhcp lease
Temp IP addr: 10.102.22.88 for peer on Interface: GigabitEthernet0/0/1
Temp sub net mask: 255.255.128.0
DHCP Lease server: 10.102.127.254, state: 4 Requesting
DHCP transaction id: 1AED16C9
Lease: 10800 secs, Renewal: 0 secs, Rebind: 0 secs
Next timer fires after: 00:00:03
Retry count: 3 Client-ID: cisco-6887.c656.d6d1-Gi0/0/1
Client-ID hex dump: 636973636F2D363838372E633635362E
643664312D4769302F302F31
Hostname: KB-VG
KB-VG#
KB-VG#show dhcp lease
Temp IP addr: 10.102.22.88 for peer on Interface: GigabitEthernet0/0/1
Temp sub net mask: 255.255.128.0
DHCP Lease server: 10.102.127.254, state: 11 Purging
DHCP transaction id: 1AED16C9
Lease: 10800 secs, Renewal: 0 secs, Rebind: 0 secs
Next timer fires after: 00:00:26
Retry count: 0 Client-ID: cisco-6887.c656.d6d1-Gi0/0/1
Client-ID hex dump: 636973636F2D363838372E633635362E
643664312D4769302F302F31
Hostname: KB-VG

TQ

MHM Cisco World · ‎10-10-2024

Debug dhcp <<- share this debug ONLY after undebug all

Thanks

MHM

Muhd · ‎10-28-2024

Hi,

Today we face back same issues, attached debug for your reference.

Flavio Miranda · ‎10-07-2024

@Muhd

This problem is probably on the ISP side and chances are you dont see any problem if the device got an IP address. ISP usually make some config on their side to avoid customer to connect something else on the link. They can filter by mac address for example or use some other security feature. I would go ahead an open a ticket with the ISP.

balaji.bandi · ‎10-10-2024

Look at the thread - 2 possibilities i see this could be bug og 17.9 code or ISP lease time.

Have you contracted the ISP and ask for Lease time they doing ?

is the DHCP Lost due to idle of the router - is the traffic always on (why not setup a simple SLA to keep ping external to keep lease up ?)

also enable debug - debug ip dhcp server events

BB

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Muhd · ‎10-28-2024

@balaji.bandi @Flavio Miranda Thanks for the reply,

Previoulsy Cisco did highlight to me about the bug, but after upgrade to recommended version 17.9.5a the issues still not resolve.
I will check with ISP regarding the lease time.

TQ

balaji.bandi · ‎10-29-2024

I can see your debug client lease time - placed lease len option: 10800

but i am bit surprised seeing this :

MAC address specified as 0000.0000.0000 (0 0). Xid is 15F6

May be try the configuration in the interface side :

ip address dhcp client-id GigabitEthernet0/0/1

#ip address dhcp client-id ?
BDI Bridge-Domain interface
GigabitEthernet GigabitEthernet IEEE 802.3z
Port-channel Ethernet Channel of interfaces
Vlan Catalyst Vlans

BB

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Cristian Matei · ‎10-29-2024

Hi,

Work with Cisco, upgrade to a recommended maintenance release that has the fix, you're obviously hitting a DHCP client bug here. From the provided output, your router, DHCP client, does not use the DHCP server provided Renew/Rebind timers, uses 0 instead of what it receives, thus it's constantly in renewal process, and the DHCP server no longer replies (ISP might have some reasonable rate-limiting there to avoid DOS against their DHCP server).

DHCP client uses a value of zero for RENEWAL and REBIND intervals:

KB-VG#show dhcp lease
Temp IP addr: 10.102.22.88 for peer on Interface: GigabitEthernet0/0/1
Temp sub net mask: 255.255.128.0
DHCP Lease server: 10.102.127.254, state: 11 Purging
DHCP transaction id: 1AED16C9
Lease: 10800 secs, Renewal: 0 secs, Rebind: 0 secs

However, looking at debug outputs, it receives non-zero values from DHCP server, with correct values, as per DHCP standard, based on offered Lease Time:

Oct 10 07:41:11.013: DHCP: Scan: Lease Time: 10800
Oct 10 07:41:11.013: DHCP: Scan: Server ID Option: 10.102.127.254 = A667FFE
Oct 10 07:41:11.013: DHCP: Scan: Renewal time: 5400
Oct 10 07:41:11.013: DHCP: Scan: Rebind time: 6000

Next, DHCP client, signals values of 0, which is illegal for DHCP client to signal that back to DHCP server, and most importantly ignores what it got from DHCP server:

Oct 10 07:41:11.014:    DHCP Lease server: 10.102.127.254, state: 4 Requesting
Oct 10 07:41:11.014:    DHCP transaction id: CB94BB84
Oct 10 07:41:11.014:    Lease: 10800 secs,  Renewal: 0 secs,  Rebind: 0 secs

As a result, DHCP client cannot use DHCP assigned IP address, it's in constant renewal and gets no answer from DHCP server:

Oct 10 07:41:19.948:             B'cast on GigabitEthernet0/0/1 interface from 0.0.0.0
Oct 10 07:41:22.949: DHCP: QScan: Timed out Requesting state%Unknown DHCP problem.. No allocation possible
Oct 10 07:41:30.981: DHCP: Waiting for 60 seconds on interface GigabitEthernet0/0/1
Oct 10 07:42:01.957: DHCP: QScan: Purging entry
Oct 10 07:42:01.957: DHCP: deleting entry 7F66D4D4AD00 10.102.22.88 from list
Oct 10 07:42:01.957: Temp IP addr: 10.102.22.88  for peer on Interface: GigabitEthernet0/0/1
Oct 10 07:42:01.957: Temp  sub net mask: 255.255.128.0
Oct 10 07:42:01.958:    DHCP Lease server: 10.102.127.254, state: 11 Purging
Oct 10 07:42:01.958:    DHCP transaction id: CB94BB84
Oct 10 07:42:01.958:    Lease: 10800 secs,  Renewal: 0 secs,  Rebind: 0 secs
Oct 10 07:42:01.958:    No timer running
Oct 10 07:42:01.958:    Retry count: 0   Client-ID: cisco-6887.c656.d6d1-Gi0/0/1
Oct 10 07:42:01.958:    Client-ID hex dump: 636973636F2D363838372E633635362E
Oct 10 07:42:01.958:                        643664312D4769302F302F31

At some point, based on DHCP server configuration, DHCP server will reply back and you start all over again.

Looks like your router correctly but randomly uses what it gets from DHCP server and it works; however some or most of the times, it does not use timers received from DHCP server, ends up in constant loop of discovery/renewal and it doesn't work.

Best,

Cristian.

Router Not Getting DHCP - Keep in Requesting &amp; Purging State

Router Not Getting DHCP - Keep in Requesting & Purging State