Troubleshooting MTU Issues - Cisco Meraki

For more information about VPN fragmentation, refer to sk98074 - MTU and Fragmentation Issues in IPsec VPN. This hotfix , adds the new kernel parameter sim_ipsec_dont_fragment . If this parameter is enabled, then the behavior of Security Gateway with enabled SecureXL changes to the following: Hello, we have a Ethernet-Link (no VPN from Checkpoint) to a network where the MTU is 1422. If we set the mtu on the interface and disable SecureXL the Clients (with default MTU of 1500) get the ICMP Fragmentation Packet and start to send packets with smaller MTU. When we reactivate SecureXL the Cl Hi, I'm investigating a fragmentation issue for a VPN on a SRX running JunOS 12.1X46-D40.2. The remote host says that it's fragmented. I have set the: set security flow tcp-mss ipsec-vpn mss 1300 Still fragmented. So I was thinking, there must be a way to check if the SRX is fragmenting the data b IKE Fragmentation - In some instances, key exchange packets can be large which will lead to packet loss as described above. By using an extension to the IKE protocol, it is possible for IPsec Peers to exchange large packets even when a trouble router exists between them.

MPLS VPN, which is the most common application, This label insertion can effectively increase the size of the original IP packet to a value more than the interface MTU, resulting in fragmentation.

[SOLVED] MTU issues in VPN connections - Networking Apr 18, 2012

Checking For Packet Fragmentation Caused by MTU

Configuring IPsec VPN Fragmentation and MTU Chapter 5 Configuring IPsec VPN Fragmentation and MTU Understanding IPsec VPN Fragmentation and MTU These notes apply to the fragmentation process: † The fragmentation process described in Figure 5-1 applies only when the DF (Don’t Fragment) bit is not set for cleartext packets entering the flow chart. Set MTU in VPN environment in case of throughput issues MTU Test in a non-VPN Environment. Example: Ping -f -l 1464 www.yahoo.com. If the ping is successful (no packet loss) at 1464 payload size, the standard MTU will be "1464 (payload size) + 20 (IP Header) + 8 (ICMP Header)" = 1492. 1464 Max packet size from Ping Test + 28 IP and ICMP headers 1492 is your optimum MTU Setting