I turn on LDP interfaces. I can ping non-fragmented packets at 1472 (1500 - 28 for headers). A TCP optimizer says to set my MTU to 1500. Pages don't load properly.

I turn off LDP interfaces. I can ping non-fragmented packets at 1472 (1500 - 28 for headers). A TCP optimizer says to set my MTU to 1500. Pages *do* load properly.

Ideas?

You have to ping with 1500 byte packets to make sure that 1500 byte packets are forwarded

MPLS adds 4 more bytes to the packet, so you need correct MPLS MTU (in this case should be at least 1504) on interfaces where LDP is running.

All MPLS MTUs and all devices between are set to 1522 MTU. All L2MTUs are 1522 or higher. I would use higher than 1522, but one of the interfaces in the network only supports 1522, so I'm having to limit everything to that.

You cannot send a ping of 1500 because of IP and ICMP headers. On a standard network with no VLANs, MPLS, etc. with the do not fragment option set, you can only send a ping with a payload of 1472 bytes. http://en.wikipedia.org/wiki/Ping#ICMP_packet

I can send a full 1472 packet in either situation. The TCP Optimizer program verifies that I have an effective 1500 byte packet when LDP is on, yet web browsing still doesn't work properly. Someone on another forum has said they haven't left version 4.x because of MPLS MTU issues.