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2
votes
1answer
238 views

Can fragments of a packet be refragmented again?

In IPv4, fragmentation is done by routers on way to the destination if DF(do not fragment) flag is not set in the IP packet. Once a packet is fragmented, its fragments may take different paths (due ...
3
votes
1answer
2k views

PIX 506E, MTU, VPN Packet Fragmentation and Shoretel IP telephone system

We have two sites, a large Southern site and a small Northern site, that have a VPN between them defined on two Cisco PIX Firewalls. Over this VPN Shoretel IP phone traffic travels as well as all ...
4
votes
1answer
785 views

Understanding Ethernet Headers, What MTU Do I Need?

I see many articles on line stating that the overhead of Ethernet is 18 bytes (example: http://www.learnios.com/viewtopic.php?f=8&t=18887) Looking at this wiki article ...
2
votes
1answer
1k views

other than manually changing it, how is MTU set?

I recently discovered a Windows 7 client that couldn't connect to one of our servers. It turned out the problem was both that the server was set for an MTU of 1514 and that the client was set to 1504. ...
2
votes
2answers
2k views

Getting interface MTU under Linux with PCAP

I am interested in storing packets I sniff using PCAP. As I preallocate the memory I need - i.e. a multiple of the MTU of the interface I am sniffing from, I would like to discover how much memory I ...
1
vote
1answer
526 views

Setting MTU Per Destination Host

I'd like to change the MTU per host as I have a mixed infrastructure where not all devices support the same MTU. I'm on OS X 10.7 and like to set some MTU per destination host and a default one.
3
votes
4answers
3k views

Is there such a thing as a “typical” or “de facto” default for MTU size?

When writing networking software, is there a default, typical, or otherwise de facto standard for MTU size, of which I should be aware? If so, what is it? Is an MTU size of 1500 (as suggested here: ...
1
vote
2answers
255 views

How can I set the MTU for just one remote server in Linux?

Hi I have a linux server that is behind a customer firewall. I can SSH into it but when I try to scp, the connection dies. I believe this is an MTU issue as described here: ...
0
votes
2answers
481 views

Computer Networks bonus: find MTU less than 1500 [closed]

This is a bonus question in my Networks class: I have to find a destination for which the path MTU < 1500 bytes. For example using the command traceroute -F www.uwaterloo.ca 1500 works, and ...
1
vote
1answer
1k views

What is the difference between IP_MTU_DISCOVER values (IP_PMTUDISC_xxx)?

The IP_MTU_DISCOVER description from "man 7 ip" is too short. As far as I understand IP_PMTUDISC_DONT/IP_PMTUDISC_DO values enable/disable packet fragmentation on a route. What are IP_PMTUDISC_WANT ...
1
vote
1answer
844 views

Configure LeftHand iSCSI SAN for jumbo frames after clients are configured

This is similar to enabling jumbo frames on an iSCSI network after the fact but in our case we configured the switches and then went through all the hosts, enabling jumbo frames (we may have screwed ...
3
votes
1answer
4k views

Is there a way of setting an MTU lower for traffic destined to a specific IP address on Cisco ASA?

I have a number of VPN sites where the MTU is lower than standard (1500). I have had at least one site where fragmentation of packets has had an effect on the success of building an IPSEC tunnel. ...
0
votes
1answer
313 views

(RFC-791) Application Layer PDU size, guaranteed to pass without fragmentation

I am writing a client-server python application, a part of which is using UDP Multicast to communicate. And my current concern is about fragmentation. RFC 791 (page 24) says: Every internet ...
2
votes
1answer
761 views

VMWare ESXi 4.1 VMXNET Ignoring MTU and Sending Jumbo Frames

On my CentOS 5.6 ESXi 4.1 VMs using VMXNET, it looks like they are attempting to send jumbo frames: However, all the interfaces are set to MTU 1500. What is causing this behavior? Update: I ...
1
vote
1answer
663 views

How do I change the MTU for only localhost connections on a Red Hat box?

I want to change the MTU value for only the connections that are going between localhost / 127.0.0.1 on a Red Hat box. How do I do that?
1
vote
1answer
661 views

different MTU sizes for bond aliases

I have a bond interface but I want to change the MTU to 1500 only for bond9:22 Is this possible? bond9:22 Link encap:Ethernet HWaddr 00:0E:0C:E4:BE:F9 inet addr:10.7.18.58 ...
5
votes
4answers
2k views

What's going on with this strange MTU?

I have a server mike at our office communicating with a remote server through a VPN. There have been various problems which seem to be linked to the MTU size. Mike is a RHEL 3 server and the customer ...
2
votes
2answers
2k views

Why do I see an IP packet with size 2960, way above the MTU setting of 1500 on the interface and it gets through?

I am analyzing traffic between a client and a Linux webserver running on a HP blade server, the client sometimes gets stuck waiting for more data when the webserver has closed the connection. The ...
1
vote
1answer
192 views

System MTU for SAN switch

I have a SAN with redundant cisco 2960s when I set it up a while ago I set all of the interfaces to use an MTU of 9000. I was looking at the config today and I noticed this line system mtu routing ...
1
vote
1answer
1k views

Optimal MTU settings ADSL for PPPoE over ATM/LLC

Is 1446 optimal for PPPoE over ATM/LLC as this forum post describes?
1
vote
1answer
276 views

MTU issue with one site only

I am currently troubleshooting an issue where some users on Windows 7 and XP systems cannot access an SSL website on our network. The same site works fine on our servers (Server 2003, completely ...
4
votes
4answers
5k views

How is the MTU is 65535 in UDP but ethernet does not allow frame size more than 1500 bytes

I am using a fast ethernet of 100 Mbps, whose frame size is less than 1500 bytes (1472 bytes for payload as per my textbook). In that, I was able to send and receive a UDP packet of message size 65507 ...
0
votes
1answer
686 views

Under FreeBSD, can a VLAN interface have a smaller MTU than the primary interface?

I have a system with two physical interfaces, combined into a LACP aggregation group. That LACP channel has two VLANs, one untagged (the "native vlan") and one using VLAN tagging. This gives us: ...
1
vote
1answer
2k views

Maximum Transmission Unit of VDSL

A simple question (hopefully) but with no clear answers when doing a Google Search. What is the MTU of VDSL (not VDSL2)? With ADSL it was 1492, but most ISPs added PPPoE/PPPoA headers reducing it to ...
2
votes
1answer
113 views

seeing remote MTUs of 250 and 68. is this ever valid?

I'm seeing an ICMP storm from a mobile phone netblocks belonging to "TELEFONICA MOVILES". Periodically we will get upwards of 5 million in a few seconds, all something like this: 08:12:05.740781 IP ...
2
votes
1answer
596 views

Telecom provider not supporting MTU higher than 1515 for leased line

We have ordered a 100 Mbps leased line and did not specify our requirement to have a minimum of 1530 MTU supported. The telco now sent us a feedback that they do not support 1530, but only 1515. Did ...
2
votes
4answers
2k views

How to check who blocks ICMP during MTU path negotiation?

I am getting MTU problems with connections to my web host provider. The issue is that I am behind ppoe with MTU size set to 1492 which preventing me from using 'scp'. Once changing MTU from 1492 to ...
4
votes
3answers
1k views

What is the Maximum MTU supported in DSL Standards

Do any of the ITU DSL standards limit the maximum MTU that can be supported? I know that RFC2516 (PPPoE) limits the MTU to 1492 bytes; however when PPPoE is not used this limit should not exist. The ...
6
votes
6answers
4k views

OpenVPN over TCP, terrible latency but only on Win7 x64

I know TCP encapsulated over TCP is a terrible idea in general, but I can deal with the occasional decreased performance and MTU issues, and the snowball effect TCP within TCP provides where error ...
3
votes
2answers
745 views

MTU, DSL router and stalling TCP

I am discovering stalling TCP connection problem. The problem arises when I try to scp stuff from remote system from my home network. My home network is connected to internet via PPPoE (ADSL+) and ...
0
votes
2answers
246 views

What should be the MTU Size for Windows Servers on the same Network

I have two windows servers on the same network, communicating to each other. What would be the best way to come up with the MTU setting?
10
votes
5answers
3k views

Are Jumbo Frames (MTU up to 9k) realistic/common over the open Internet?

I've got an application that would benefit from larger Ethernet frames. (In theory, we could reduce the number of outbound packets by > 50%, maybe even 66%.) I'm also in the process of specifying ...
1
vote
1answer
1k views

VLAN MTU on Linux with Intel Pro/1000 PT Server Adapter

For some reason MTU still seem to be an occasional issue with trunked connections. In this case I have a trunk connected to an Enterprise Linux 5 server. I use standard vlan seperation in Linux, and ...
3
votes
3answers
9k views

MTU problems? 'Request timed out'

I've been trying to figure out why some(very few) of the people who visit my site have random slowdowns and error pages('page cannot be loaded'). The random slowdowns and error pages never happen for ...
1
vote
2answers
187 views

Weird network interaction between Vista and Ubuntu

I have a network where my WAN (a CableModem) goes into a (dubiously configured) Ubuntu box which acts as the router for the whole company. We recently switched our ISP, and we're getting a very weird ...
15
votes
2answers
2k views

Why does lowering the MTU from 1500 to 1499 allow me to access most websites?

I had this issue where I was only able to connect to websites like google.com and ibm.com when the mtu was set at 1500, but if I tried to connect to anything else, it would just show a blank page. ...
4
votes
3answers
1k views

What IP MTU sizes are seen in real networks

I am writing an application which will be deployed in third party networks. It will receive IP packets and I want to know what the maximum size in reality they are likely to be is. I'm not asking what ...
4
votes
3answers
3k views

What's the best MTU setting for a web server?

I manage several web servers and their MTU settings were set at 1500 by default. Some of the machines have an MTU setting of 576. I've read a bunch about MTU and I feel I understand it well enough but ...
3
votes
3answers
10k views

How to increase MTU size on Linux 2.6?

How to increase MTU size on Linux 2.6? Is such a thing possible? If yes, which files (in /etc or elsewhere) must one edit?