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Some DHCP Users Failed to Access the Internet Although They Successfully Obtained IP Addresses

Publication Date:  2013-09-27 Views:  62 Downloads:  0
Issue Description
Some DHCP users connected to an ME60 V6R2 successfully obtained IP addresses, but failed to access the Internet. Pinging the gateway or DNS failed. After the network interface card (NIC) on a problematic PC was restarted several times (or network cables were disconnected and inserted several times), the problem did not occur.
Handling Process

Huawei completed the following steps to diagnose the problem:

1. Issued dis access-user to check whether the affected users were online. They were online.
2. Checked the ARP logs of an affected host. The host failed to learn the MAC address of the gateway.
3. Traced the messages of the host on the gateway. The gateway received ARP requests from the host, but did not return any response.
4. Issued display arpbas slot 3 ip-address in the hidden view to query the IP address information of the host. No ARP entries existed.

5. Queried diagnostic logs.
The following information was found:
Fail to insert hash node because of exceeding the maximal arp spec 32768[AddUserByUcm]Failed to insert hash node for new user

6. Checked the maintenance operations performed before the problem occurred.
Multiple static users were added.
7. Issued display static-user to get the number of static users by slot. The number of static users configured for the interface board reached 28k. An interface board on an ME60 V6R2 supports a maximum of 32k ARP entries, each of which is shared by a static user and a DHCP user. Static users consumed fixed ARP entries, so remaining ARP entry resources were insufficient. As a result, ARP resources failed to be allocated to DHCP users.
8. Deleted redundant static user data to reserve 5k ARP entries. The DHCP users can access the Internet.
Root Cause
ARP entry resources do not suffice for allocating ARP resources to DHCP users.
Delete redundant static user data to release ARP entry resources.
a. The real cause was insufficient ARP entry resources, not restarting the NIC. If a user went offline while an NIC was restarted, ARP entry resources were released, so the affected user got online.
b. In V6R2, an interface board supports a maximum of 32k ARP entries. In V1R6, the threshold is 16k. After the system prompts that no more static users can be added, services of DHCP users may be affected. Therefore, do not configure too many static users.