Cisco Virtual Security Gateway for Nexus 1000V Series Switch Troubleshooting Guide, Release 4.2(1)VSG1(4.1)

Displaying VEM Information

Use the following commands to display Virtual Ethernet Module (VEM) information:

• vemlog— Displays and controls VEM kernel logs
• vemcmd— Displays configuration and status information
• vem-support all— Displays support information
• vem status— Displays status information
• vem version— Displays version information
• vemcmd show arp all — Displays the ARP table on the VEM
• vemcmd show vsn config — Displays all the Cisco VSGs configured on the VEM and the Cisco VSG licensing status (firewall on or off)
• vemcmd show vsn binding — Displays all of the VM LTL ports to the Cisco VSG bindings
• vemcmd show learnt — Displays all of the VMs that have been learned by the VEM

Displaying Miscellaneous VEM Details

These commands provide additional VEM details:

• vemlog show last number-of-entries — Displays the circular buffer

This example shows how to display the number of entries in the circular buffer:

• vemlog show info— Displays information about entries in the log

This example shows how to display log entries:

• vemcmd help— Displays the type of information you can display

This example shows how to display the vemcmd help:

show vservice node brief Command Output Indicates Service Node State is Down

This section includes the following topics:

Cisco VSG with a VN Service vmknic in Layer 3 Mode

Cisco VSGs with Multiple l3-vn-service vmknics in Layer 3 Mode

Cisco VSG with a VN Service vmknic in Layer 3 Mode

When encapsulated traffic that is destined to a Cisco VSG is connected to a different subnet other than the vmknic subnet, the VEM does not use the VMware host routing table. Instead, the vmknic initiates an Address Resolution Protocol (ARP) for the remote Cisco VSG IP addresses.

You must configure the upstream router to respond by using the proxy ARP feature. If the proxy ARP feature is not configured on the upstream router, the ARP fails and the show vservice node brief indicates that the service node state is down.

To resolve this issue configure the proxy ARP feature on the router as follows:

Cisco VSGs with Multiple l3-vn-service vmknics in Layer 3 Mode

The data path traffic and the ARP packets for the Cisco VSGs in Layer 3 mode can use any vmknic that is configured on the VEM host for packet forwarding to the Cisco VSG when you enter the capability l3-vn-service command.

Therefore, all vmknics that are on a VEM host must be able to reach all Cisco VSGs in Layer 3 mode.

If a router is between the vmknics and the Cisco VSGs, all vmknics must have an interface in the router network (VLAN), and all the Cisco VSGs in the Layer 3 mode must have an interface in the router network (VLAN) to ensure that each vmknic has a route to each Cisco VSG.

To resolve this issue ensure that all l3-vn-service vmknics can reach all the Cisco VSGs in the Layer 3 mode that are used by the VEM host.

Note You must enable Proxy ARP on all the interfaces of the router that is alongside the vmknics.

Traffic with Large Payloads Fails: ICMP Too Big Message Does Not Reach the Client with the Cisco VSG in Layer 3 Mode

If a router lies between the vmknic and the Cisco VSG in the Layer 3 mode, and the router receives a packet that it cannot forward due to a large packet size, the router generates an ICMP Too Big message for the vmknic. The vmknic cannot forward the ICMP Too Big message of the router to the client and the vmknic drops the message. The client never receives the ICMP Too Big message and cannot refragment the packet for successful end-to-end traffic and the end-to-end traffic fails. This problem is typically seen if the router interface to the VEM is set at a higher maximun transmission unit (MTU) than the router interface to the Cisco VSG. For example, the router interface to the VEM has an MTU of 1600 and the interface to the Cisco VSG has an MTU of 1500.

This problem can be seen as an increase in the ICMP Too Big Rcvd counter in the show vservice statistics command.

To resolve this issue, configure an oversized MTU (for example, 1600) on both of the router interfaces.

End-to-End Traffic with the Cisco VSG in Layer 3 Mode Fails

When the VEM communicates with the Cisco VSG in the Layer 3 mode, an additional header with 82 bytes is added to the original packet. The VEM does not support fragmentation in the Layer 3 mode and the ports or network elements (which carry a vPath encapsulated packet) must be configured in such a way that the vPath overhead is accommodated.

If end-to-end traffic fails with a Cisco VSG Layer 3 mode, set the uplink MTU to 1582 bytes to accommodate the additional overhead. This solution assumes that the client and server VM MTUs are at the default of 1500 bytes.

End-to-End Traffic with the Cisco VSG in Layer 3 Mode and Jumbo Frames Fails

Traffic with the Layer 3 encapsulation fails even with the uplink MTU set to 9000 bytes.

If jumbo frames are enabled in the network and the end-to-end traffic fails, make sure that the MTU of the client and server VMs are 82 bytes smaller than the uplink. For example, if the uplink MTU is 9000, set the MTU of the client and server VMs to 8918 bytes.

TCP State Checks

By default, TCP state checks are disabled in vPath for the traffic protected by the Cisco VSG. Sometimes, you might see delays in the TCP traffic. To diagnose TCP state checks related issues, you need to enable TCP state checks.

Check the following counters at the VSM in the show vservice statistics output:

vsm# show vservice statistics | grep "TCP chkfail"

TCP chkfail InvalACK 0 TCP chkfail SeqPstWnd 0
TCP chkfail WndVari 0

This example shows how to enable the TCP state checks on a VSM:

Connection Limit in the Cisco VSG

The Cisco VSG can have up to 256,000 active connections at any given point of time. If for some reason new connections slows down or connections see too many failures, you can check the Cisco VSG for any connection limits that it experiences. If the VEM-to-Cisco VSG connection is not smooth or have some issues that indicates that the Cisco VSG might have missed a few updates from vPath which results in an accumulation of large active connections in its flow table.

This example shows how to check the active connection count on the Cisco VSG:

vsg# show service-path statistics | inc "Active Connections"

Active Flows 48 Active Connections 24

Debugging the Traffic Flow Via a Service Chain

When configured, the service-chain functionality enables traffic to flow through the Cisco VSG and the Cisco ASA 1000V clould firewall. The Cisco VSG monitors the data packets and authorizes its flow from the VM to the destination ports. The VM and Cisco ASA 1000V are always in the same broadcast domain, that is, either a VLAN or a Virtual Extensible Local Area Network (VXLAN).

To debug the traffic flow via the service chain, follow these steps:

Step 1 Make sure that the VM’s default gateway is set to the ASA 1000V inside interface and is reachable.

Step 2 On the VSM, ensure that the Cisco VSG and ASA 1000V are alive, which ensures that the vPath is able to reach the service nodes.

Step 3 On the VSM, check a connection’s status of action (SAct).

In the SAct value Pp, the uppercase ‘P’ indicates the action that is initiated by the Cisco VSG, while the lowercase ‘p’ indicates the action that is deduced based on the returning traffic from the ASA V1000. If the SAct value is ‘rr,’ it indicates that the traffic is redirecting to either the Cisco VSG or the ASA V1000 but no response is being received.

Step 4 On the VSM, verify that the service node version information (VVer) is ‘2’ so that it works in the service-chain.

Troubleshooting the Service Chain by Excluding the Cisco VSG Node

The service-chain configuration has the Cisco VSG and ASA 1000V nodes in its service path for a given traffic flow. For debugging purposes, the Cisco VSG can be removed temporarily from the node configuration to isolate a problem. Thus, a user can verify the traffic flow with just the ASA 1000V. Later, the Cisco VSG can be added again to restore the original service-chain configuration using the two said service nodes.

VEM/vpath Configured Correctly on a VEthernet Interface for a ServiceChain

You can use the module vem vem-num execute vemcmd show vsn bindings command on the VSM to ensure that the bindings are correctly configured on the VEM for a service chain. Two entries appear for a single LTL — one of each service node must be displayed.

Cisco VSG on a VXLAN is not working

The Cisco VSG node can be configured with a VXLAN in the Layer 2 mode only. Make sure that the adjacency is correctly defined as Layer 2 and the bridge-domain configuration is valid. The show service node brief command can be used to check a service node’s state with respect to the vPath.

This example shows a Cisco VSG node configuration for a VXLAN:

This example shows how to display the node status in a VXLAN: