Dell EMC Configuration Guide for the S3100 Series 9.14.2.4

Guidelines for Enabling the VLT Proxy Gateway

A typical scenario is virtual movement of servers across data centers. Virtual movement enables live migration of running virtual machines (VMs) from one host to another without downtime. For example, consider a square VLT connecting two data centers. If a VM, VM1 on Server Rack 1 has C as its default gateway and VM1 performs a virtual movement to Server Rack 2 with no change in default gateway. In this case, L3 packets destined for C can be routed either by C1 or D1 locally. To do this, install the local system mac address of C and D in both C1 and D1 so the packets for C and D could have a hit at C1 /D1 and be routed locally.

For more information about eVLT, refer to the Virtual Link Trunking (VLT) chapter. The core or Layer 3 routers C and D in local VLT Domain and C1 and D1 in the remote VLT Domain are then part of a Layer 3 cloud.

Keep the following points in mind when you enable a VLT proxy gateway:

• Proxy gateway is supported only for VLT; for example, across a VLT domain.
• You must enable the VLT peer-routing command for the VLT proxy gateway to function.
• Asymmetric virtual local area network (VLAN) configuration, such as the same VLAN configured with Layer 2 (L2) mode on one VLT domain and L3 mode on another VLT domain is not supported. You must always configure the same mode for the VLANs across the VLT domain.
• You must maintain VLAN symmetry within a VLT domain.
• The connection between DCs must be a L3 VLT in eVLT format . For more information, refer to the eVLT Configuration Example
• The trace route across the DCs can show extra hops.
• To ensure no traffic drops, you must maintain route symmetry across the VLT domains. When the routing table across DCs is not symmetrical, there is a possibility of a routing miss by a DC that does not have the route for L3 traffic. Because routing protocols are enabled and both DCs are in the same subnet, there is no dynamic route asymmetry. But if you configure a static route on one DC and not on the other, there is asymmetry.
• If the port-channel specified in the proxy-gateway command is not a VLT LAG, the configuration is rejected by the CLI.
• You cannot change the VLT LAG to a legacy LAG when it is part of proxy-gateway.
• You cannot change the link layer discovery protocol (LLDP) port channel interface to a legacy LAG when you enable a proxy gateway.
• Dell EMC Networking recommends the vlt-peer-mac transmit command only for square VLTs without diagonal links.
• The virtual router redundancy (VRRP) protocol and IPv6 routing is not supported.
• Private VLANs (PVLANs) are not supported.
• When a Virtual Machine (VM) moves from one VLT domain to the another VLT domain, the VM host sends the gratuitous ARP (GARP) , which in-turn triggers a mac movement from the previous VLT domain to the newer VLT domain.
• After a station move, if the host sends a TTL1 packet destined to its gateway; for example, a previous VLT node, the packet can be dropped.
• After a station move, if the host first PINGs its gateway; for example, a previous VLT node it results in a 40 to 60% success rate considering it takes a longer path.
• When you remove and add back a MAC address, L3 frames can be received out-of-order at the L3 cloud. This happens when proxy gateway routing and sub-optimal routing intersperse with each other.

Enable VLT Proxy Gateway

To enable the VLT proxy gateway, the system mac addresses of C and D in the local VLT domain must be installed in C1 and D1 in the remote VLT domain and vice versa. You can install the mac address in two methods - the proxy-gateway lldp method or the proxy-gateway static configuration. Proxy-gateway LLDP is a dynamic method of installing the local mac addresses in the remote VLT domain, which is achieved using a new organizational type, length, value (TLV) in LLDP packets.

LLDP Organizational TLV for Proxy Gateway

• You can configure the VLT proxy gateway in a VLT domain using the proxy-gateway LLDP command in proxy-gateway Configuration mode. Specify the port-channel interface of the square VLT link on which LLDP packets are sent using thepeer-domain-link port-channel command.

  Configuring the proxy gateway lldp and the peer-domain-link port channel, LLDP sets TLV flags on the interfaces for receiving and transmitting private TLV packets. After defining these organizational TLV settings, LLDP encodes the local system mac-addresses as organizational TLVs for transmitting to the peer. If you specify the no proxy gateway LLDP interface command, LLDP stops transmitting and receiving proxy gateway TLV packets on the specified interfaces. However, other TLVs are not affected. From the interfaces on which you enabled the proxy gateway LLDP, LLDP decodes the TLV packets from the remote LLDP by using the new organizational TLV.

  The following requirements must be satisfied for LLDP proxy gateway to function correctly:

  • Data centers must be directly connected.

  • LLDP has a limited TLV size. As a result, information that is carried by the new TLV is limited to one or two MAC addresses.

  • You must have all related systems properly configured and set up.

• LLDP defines an organizationally specific TLV (type 127) with a unique identifier (0x0001E8) and a defined subtype (0x01) for sending or receiving information.

• LLDP uses the existing infrastructure and adds a new TLV for sending and receiving on the configured ports.

• There are only a few MAC addresses for each unit transmitted. All currently active MAC addresses are carried on the newly defined TLV.

• Dell EMC Networking devices not configured with VLT proxy gateway process standard TLVs and ignore TLVs configured with VLT proxy gateway.

The LLDP organizational TLV passes local destination MAC address information to peer VLT domain devices so they can act as a proxy gateway. To enable proxy gateway LLDP, two configurations are required:

• You must configure the global proxy gateway LLDP to enable the proxy-gateway LLDP TLV.

• You must configure the interface proxy gateway LLDP to enable or disable a proxy-gateway LLDP TLV on specific interfaces.

• The interface is typically a VLT port-channel that connects to a remote VLT domain.

• The new proxy gateway TLV is carried on the physical links under the port channel only.

• You must have at least one link connection to each unit of the VLT domain.

Following are the prerequisites for Proxy Gateway LLDP configuration:

• You must globally enable LLDP.

• You cannot have interface–level LLDP disable commands on the interfaces configured for proxy gateway and you must enable both transmission and reception.

• You must connect both units of the remote VLT domain by the port channel member.

• If you connect more than one port to a unit of the remote VLT domain, the connection must be completed by the time you enable the proxy gateway LLDP.

• You cannot have other conflicting configurations (for example, you cannot have a static proxy gateway configuration).

Proxy Gateway LLDP configuration might not operate properly if one of the following conditions is true:

• Any proxy gateway configuration or LLDP configuration is not working.

• LLDP packets fail to reach the remote VLT domain devices (for example, because the system is down, rebooting, or the port’s physical link connection is down).