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Viptela Documentation

tcp-mss-adjust

vpn interface tcp-mss-adjust—Configure the maximum segment size (MSS) of TCP SYN packets passing through a device. By default, the MSS is dynamically adjusted based on the interface or tunnel MTU such that TCP SYN packets are never fragmented. For data sent over an interface, the MSS is calculated by adding the interface MTU, the IP header length, and the maximum TCP header length. For data sent over a tunnel, the MSS is the sum of the tunnel MTU, the IP header length, and the maximum TCP header length.

vManage Feature Template

For all Viptela devices:

Configuration ► Templates ► VPN Interface Bridge
Configuration ► Templates ► VPN Interface Cellular (for vEdge cellular wireless routers only)
Configuration ► Templates ► VPN Interface Ethernet
Configuration ► Templates ► VPN Interface GRE
Configuration ► Templates ► VPN Interface PPP
Configuration ► Templates ► VPN Interface PPP Ethernet

Command Hierarchy

vpn vpn-id 
  interface interface-name    
    tcp-mss-adjust bytes

Options

Change the Packet Size
bytes
TCP maximum segment size (MSS), which is the largest amount of data that the interface can receive in a single IP datagram, excluding the TCP and IP headers.
Range: 552 to 1960 bytes; for PPP interface, 552 to 1452 bytes
Default: None

Operational Commands

show interface

Example

Set the TCP MSS:

vEdge# config
Entering configuration mode terminal
vEdge(config)# vpn 0 interface ge0/1
vEdge(config-interface-ge0/1)# tcp-mss-adjust 1400
vm5(config-interface-ge0/1)# commit and-quit 
Commit complete.
vEdge# show interface 

                                  IF      IF                                                                TCP                                   
                                  ADMIN   OPER    ENCAP                                      SPEED          MSS                 RX       TX       
VPN  INTERFACE  IP ADDRESS        STATUS  STATUS  TYPE   PORT TYPE  MTU   HWADDR             MBPS   DUPLEX  ADJUST  UPTIME      PACKETS  PACKETS  
-----------------------------------------------------------------------------------------------------------------------------------------------
0    ge0/0      10.1.15.15/24     Up      Up      null   transport  1500  00:0c:29:7d:1e:fe  10     full    1420    0:04:12:25  202419   218746
0    ge0/1      10.1.17.15/24     Up      Up      null   service    1500  00:0c:29:7d:1e:08  10     full    1400    0:04:04:10  448      5     
0    ge0/2      -                 Down    Up      null   service    1500  00:0c:29:7d:1e:12  10     full    1420    0:04:12:33  448      0     
0    ge0/3      10.0.20.15/24     Up      Up      null   service    1500  00:0c:29:7d:1e:1c  10     full    1420    0:04:04:10  453      5     
0    ge0/6      57.0.1.15/24      Up      Up      null   service    1500  00:0c:29:7d:1e:3a  10     full    1420    0:04:04:10  448      4     
0    ge0/7      10.0.100.15/24    Up      Up      null   service    1500  00:0c:29:7d:1e:44  10     full    1420    0:04:10:19  1044     594   
0    system     172.16.255.15/32  Up      Up      null   loopback   1500  00:00:00:00:00:00  10     full    1420    0:04:03:49  0        0     
1    ge0/4      10.20.24.15/24    Up      Up      null   service    1500  00:0c:29:7d:1e:26  10     full    1420    0:04:04:07  2009     1603  
1    ge0/5      56.0.1.15/24      Up      Up      null   service    1500  00:0c:29:7d:1e:30  10     full    1420    0:04:04:07  448      4     
512  eth0       10.0.1.15/24      Up      Up      null   service    1500  00:50:56:00:01:0f  1000   full    0       0:04:12:18  7581     4581

Release Information

Command introduced in Viptela Software Release 14.1.​
Starting with Release 15.3, the TCP SYN MSS is dynamically adjusted based on the interface or tunnel MTU.
In Release 16.3, maximum TCP MSS changed from 1460 bytes to 1960 bytes.

Additional Information

See the Segmentation CLI Reference article for your software release.
system-tunnel-mtu

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