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4
votes
1answer
134 views

Relationship between MTU and NFS rsize/wsize options

I'm trying to understand networking settings related to NFS and various buffer sizes (and there are quite a few). I'm running wireshark and inspecting the TCP packets arriving at the NFS server. ...
0
votes
0answers
37 views

Throughput decreases after MTU 5000

I am trying to test throughput between two computers directly connected through 1 Gb and testing with iperf. I am getting a throughput around 980Mbps when MTU is between 5000 and 5050, however it ...
1
vote
1answer
149 views

Cisco IPSEC VPN Slow Speeds

We have a site to site IPSEC VPN, both endpoints are Cisco PIX 515e's. The links at both end are 100mb, however speeds over the VPN (logged using jperf) are at most 4mb. Obviously this represents a ...
0
votes
0answers
73 views

Severe performance issues sharing openvpn client connection to LAN clients virtualbox

I am trying to set up an internal network in Virtualbox in order to share an openvpn client tunnel with multiple VMs acting as clients that should be completely isolated from everything except for the ...
2
votes
1answer
62 views

Maximum MTU size

Thought one of the issues I'm experiencing with the following question is due to MTU rightfully so. ESXi 5 VM Putty session hangs, vSphere client timing out However, when I tried testing the ...
1
vote
1answer
284 views

How do I view cached PMTU under Linux (and all other OSs)

When I ping a remote site with the DF bit set and a packet size that is too big for my router the first ICMP "fragmentation required" message is sent from the router. After that the message comes from ...
2
votes
2answers
348 views

SFTP fails on listing directories with large number of files

I try to connect to an sftp server (vsftpd) on Centos server through port 22. there is no problem in connection and initial directory listing; there is also no problem if I click on a directory with ...
-4
votes
1answer
57 views

How to maximize mtu size for SunOS 5.10 Generic_147440-26 sun4v sparc sun4v [closed]

Despite installing and enabling the 10G fiber card, data copy or transfer is still happening on a 1G rate.
2
votes
1answer
83 views

IPv6: using a link mtu greater than the mtu of the default route

When configuring an IPv6 LAN it may be desirable to use router advertisements to announce a link MTU of either the standard 1500 bytes or something larger to enable usage of jumbo frames, perhaps ...
1
vote
1answer
90 views

How do I force a specific MTU for only certain TCP ports?

Background I have a set of embedded hardware deployed in the field. These remote machines connect back to my servers at AWS running Ubuntu and I use the iptables mangle chain to lower the MTU to 500 ...
1
vote
3answers
305 views

disadvantages MTU over 1500

What disadvantages have to set the MTU to the maximum possible value in ALL network adapters on a network (including virtual switches vmware esx)? Why do not the producers as a default? I do not ...
0
votes
1answer
241 views

What is the right way to temporarily disable/enable PMTU Discovery on a Linux box?

I've a few pcaps that contain packets larger than standard ethernet MTU size of 1500B. I searched about this and found refs pointing towards Jumbo Frames. I now understand that since I'm on a GBE ...
1
vote
4answers
677 views

Smaller network packets vs bigger packets - confused

Some are saying that bigger packets are better to send then smaller. But in this app: http://media.pearsoncmg.com/aw/aw_kurose_network_2/applets/message/messagesegmentation.html The lower the packet ...
0
votes
1answer
130 views

Jumbo Frame configuration & VMware

I am hoping one of you can help clear up some of my confusion on this matter. We have 2 new catalyst 3750 switches to support our VM hosts and SAN arrays. The SAN arrays utilize jumbo frames with an ...
2
votes
0answers
979 views

How do I prevent TCP connection freezes over an OpenVPN network?

New details added at the end of this question; it's possible that I'm zeroing in on the cause. I have a UDP OpenVPN-based VPN set up in tap mode (I need tap because I need the VPN to pass multicast ...
0
votes
1answer
727 views

openvpn TCP/UDP slow SSH/SMB performance

I have question about strange behavior of my openVPN configuration on Debian lenny. I have 2 server configs (one proto tcp-server based and one proto udp based). ISP bandwidth is 7Mbit/7Mbit. When I ...
8
votes
2answers
1k views

Jumbo frames between KVM guest and host?

I am trying to implement a 9000 byte MTU for storage communication between KVM guests and the host system. The host has a bridge (br1) with a 9000 byte MTU: host# ip link show br1 8: br1: ...
1
vote
1answer
1k views

Linux - set an interface to not fragment packets

I am using a Linux as a router. The machine has two NICs. This router will be used for experiments, so I have set one of it's interfaces to have a MTU that is lower than the standard (let's decide ...
-1
votes
1answer
145 views

centos 5.6, virtual on Vsphere

suddenly my virtual centos server (5.6 on VMWare-VSphere) is not working... It started with the url not responding, nor the ip. (NO HTTP response, no ping). When I entered on the server via ssh to ...
0
votes
1answer
42 views

Finding network type using MTU

For example MTU of Ethernet is 1500. Now if the packets are fragmented, then observed MTU will be the MTU of the router (i.e. less than 1500). Is there any method to find out the type of the client ...
2
votes
1answer
217 views

MTU value causing applications to hang

I am using CentOS 5 in my environment and it acts as a gateway for my LAN. My eth0 interface MTU is set to 1500 (default). UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Recently I am facing a ...
17
votes
2answers
5k views

What is the “in-the-wire” size of a ethernet frame? 1518 or 1542?

According to the table here, it says that MTU = 1500 bytes and that the payload part is 1500 - 42 bytes or 1458 bytes (<- this is actually wrong!). Now on top of that you have to add IPv4 and UDP ...
0
votes
0answers
430 views

ICMP ping size stops working at 1272 bytes

I am pinging between two servers. These are both connected with 100Mbps ethernet NICs to the same switch. As you can see from the results below, I can ping from one to the other giving an ICMP data ...
13
votes
1answer
1k views

What am I misunderstanding about calculating MTU?

Okay, I just finished resolving a jumbo frames issue between a few Xserves, a Netgear GSM7224, and a Drobo B800i. It turned out that the Xserves (Mac OS X 10.6.8 Server) and the Drobo B800i accept the ...
4
votes
2answers
184 views

Impact of MTU on IP packet fragmentation and reassembly

Let's say computer S (sender) sends some IP packets to computer R (receiver). Between S and R, there are 6 networks, divided by 5 routers. So the IP packets leave R, go through network 1, pass router ...
2
votes
1answer
162 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
1k 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 ...
0
votes
0answers
2k views

VPN Issues when uploading files - MTU issue?

I have a PPTP server setup at home, which I connect to from my work's network. I can connect to it without any issue, but when I try to upload files, I lose connectivity to it about 1mb into the ...
4
votes
1answer
443 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
624 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
616 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
326 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
887 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
181 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
315 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 ...
0
votes
1answer
773 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
629 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
2k 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
236 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
625 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
400 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
393 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 ...
4
votes
3answers
1k 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
1answer
1k 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
169 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 ...
0
votes
1answer
715 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
247 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 ...
3
votes
3answers
2k 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
541 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
1k 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 ...