Kitz ADSL Broadband Information
adsl spacer  
Support this site
Home Broadband ISPs Tech Routers Wiki Forum
 
     
   Compare ISP   Rate your ISP
   Glossary   Glossary
 
Please login or register.

Login with username, password and session length
Advanced search  

News:

Author Topic: Fantasy future jumbo MRU / MTU  (Read 2559 times)

Weaver

  • Addicted Kitizen
  • *****
  • Posts: 9114
  • Retd sw dev; A&A; 4 × 7km ADSL2; IPv6; Firebrick
Fantasy future jumbo MRU / MTU
« on: September 20, 2016, 08:14:13 PM »

I wonder if there will ever be an opportunity to start to replace the 1500 byte MRU / MTU across the internet. There are of course some jumbo LANs with ~9000 byte frame sizes allowed.

If we were ever to start making the change what would the next step up be? Up to 9k? To just under 64k? More? (I have this vague recollection that some protocols might start to break if we get near to 64k, because of field size limits, can't remember though.)

It's obviously a good thing if routers and switches have to process fewer packets per second. And ram is cheaper. On the other hand, long queuing delays are very bad, so sane queuing policy and good design would be a must, but then that's just another way of saying don't design things badly.

Of course, some use-cases would possibly want to keep packet sizes down because of real-time considerations. (Revisit the considerations behind the design of ATM.)

Somehow I can't see that 1500 bytes is going to be an ideal choice for decades to come, so perhaps now would be the time to start, saying that all new good Internet core routers should handle x byte packets. Testing might be a problem, as getting complete joined up end-to-end paths would be needed before experience could be gained from large-scale real-world field testing outside big labs with controlled kit.
Logged

Chrysalis

  • Content Team
  • Addicted Kitizen
  • *
  • Posts: 6328
Re: Fantasy future jumbo MRU / MTU
« Reply #1 on: September 20, 2016, 08:29:26 PM »

even after the standardisation of 1500 byte mtu there is still issues with some routers and endpoints needing smaller sizes.

jumbo frames exists but like ipv6 it will take time for things to progress.
Logged
AAISP - Billion 8800NL bridge & PFSense BOX running PFSense 2.4 - ECI Cab - LINE STATISTICS CLICK HERE

aesmith

  • Kitizen
  • ****
  • Posts: 1010
Re: Fantasy future jumbo MRU / MTU
« Reply #2 on: January 07, 2017, 01:44:41 PM »

Server and storage guys used to make a big deal about jumbo frame support, presumably by comparison with Fibre Channel with its 16K frame size.  However in reality may data centres using IP storage (iSCSI or NFS) tend not to bother.   It can cause issues, for example we diagnosed a problem with Lync conferencing over the WAN (everything's a network problem) and found that the stupid Lync server was sending out it's media in jumbo frames with don't fragment set.
Logged

Weaver

  • Addicted Kitizen
  • *****
  • Posts: 9114
  • Retd sw dev; A&A; 4 × 7km ADSL2; IPv6; Firebrick
Re: Fantasy future jumbo MRU / MTU
« Reply #3 on: October 10, 2020, 02:02:36 PM »

Assuming enough support is found, hypothetically; how would we make the change? Got to start somewhere, where would that be?

Another question which is not the same thing: I read something somewhere about BT systems being capable of handling 1600 byte long xPDUs ( perhaps L2-PDUs ). Very good thing; not in the range proposed here of course, but extremely helpful. Does this ring any bells?
Logged

CarlT

  • Kitizen
  • ****
  • Posts: 1697
  • Software Defined WAN deployment engineer
Re: Fantasy future jumbo MRU / MTU
« Reply #4 on: October 11, 2020, 10:57:36 PM »

The core routers already support jumbo frames and carry bigger PDUs than 1500 bytes as on top of Ethernet there are 32 bit MPLS headers.

The 1500 bytes is going nowhere. A fair amount of traffic uses less that 1500 bytes and links are so large overheads are virtually inconsequential.

Jumbo is only used for data replication, usually across long distances at high bandwidth, with private lines with 0% loss SLAs and that's reasonable.

For now the 1500 bytes remains a good compromise between minimal overheads and the diminishing returns as data needs retransmission over unreliable networks.
Logged
WiFi: Nighthawk® AX12 RAX120
Routing: pfSense VM
Switching: Mikrotik 2* CRS305-1G-4S-IN, 1 * CRS309-1G-8S+; various cheap and cheerful TP-Link/Netgear
Exchange: Wakefield
ISP: BT Full Fibre 900. Zen Full Fibre 900.

Weaver

  • Addicted Kitizen
  • *****
  • Posts: 9114
  • Retd sw dev; A&A; 4 × 7km ADSL2; IPv6; Firebrick
Re: Fantasy future jumbo MRU / MTU
« Reply #5 on: October 11, 2020, 11:55:52 PM »

Thanks Carl. How much of the path would you say is MTU > 1600 bytes ?
Logged

CarlT

  • Kitizen
  • ****
  • Posts: 1697
  • Software Defined WAN deployment engineer
Re: Fantasy future jumbo MRU / MTU
« Reply #6 on: October 12, 2020, 12:09:50 PM »

Hard to say as it's far from uncommon now for routers to implement jumbo frame support automatically when an oversized frame arrives.

Cisco's ASR 9000 series for instance do this - they increment a counter for an oversized frame if it arrives on an interface at default MTU and send it across regardless, fragmenting it if necessary for the next hop.
Logged
WiFi: Nighthawk® AX12 RAX120
Routing: pfSense VM
Switching: Mikrotik 2* CRS305-1G-4S-IN, 1 * CRS309-1G-8S+; various cheap and cheerful TP-Link/Netgear
Exchange: Wakefield
ISP: BT Full Fibre 900. Zen Full Fibre 900.

Weaver

  • Addicted Kitizen
  • *****
  • Posts: 9114
  • Retd sw dev; A&A; 4 × 7km ADSL2; IPv6; Firebrick
Re: Fantasy future jumbo MRU / MTU
« Reply #7 on: October 12, 2020, 07:58:21 PM »

But they can handle oversized frames if the next hop can?

I don’t understand the counter; assuming it’s concerned with the fragmentation ? Seems a strange thing to do. I would have kept an amount_still_to_be_sent counter
Logged

CarlT

  • Kitizen
  • ****
  • Posts: 1697
  • Software Defined WAN deployment engineer
Re: Fantasy future jumbo MRU / MTU
« Reply #8 on: October 12, 2020, 11:58:26 PM »

The counter is nothing to do with handling the actual frame it's just to indicate that an oversized frame arrived.

Usually you wouldn't expect to see those on core network as the edge, either customer or provider, should be cutting things down to size.

Points to a configuration mismatch. Noteworthy.

You might find Link Layer Discovery Protocol / LLDP / 802.1AB an interesting read.
Logged
WiFi: Nighthawk® AX12 RAX120
Routing: pfSense VM
Switching: Mikrotik 2* CRS305-1G-4S-IN, 1 * CRS309-1G-8S+; various cheap and cheerful TP-Link/Netgear
Exchange: Wakefield
ISP: BT Full Fibre 900. Zen Full Fibre 900.

Weaver

  • Addicted Kitizen
  • *****
  • Posts: 9114
  • Retd sw dev; A&A; 4 × 7km ADSL2; IPv6; Firebrick
Re: Fantasy future jumbo MRU / MTU
« Reply #9 on: October 13, 2020, 06:49:45 AM »

Got it, thanks. Will enjoy reading matter.
Logged

burakkucat

  • Global Moderator
  • Senior Kitizen
  • *
  • Posts: 30804
  • Over the Rainbow Bridge
    • The ELRepo Project
Re: Fantasy future jumbo MRU / MTU
« Reply #10 on: October 13, 2020, 05:00:41 PM »

You might find Link Layer Discovery Protocol / LLDP / 802.1AB an interesting read.

b*cat takes note and downloads a copy of the document.
Logged
:cat:  100% Linux and, previously, Unix. Co-founder of the ELRepo Project.

Please consider making a donation to support the running of this site.

Alex Atkin UK

  • Kitizen
  • ****
  • Posts: 1652
    • My Broadband History
Re: Fantasy future jumbo MRU / MTU
« Reply #11 on: October 14, 2020, 11:22:54 PM »

b*cat takes note and downloads a copy of the document.

Can you translate it for us dumb humans?  I noticed my main switch uses LLDP but haven't a clue what any of it means.
Logged
INTAKE (ECI) Zen: Home Hub 5A OpenWrt Plusnet: VMG-3925-B10B Three 4G: Hauwei B535-232 Router: pfSense (i5-7200U) WiFi: Ubiquiti nanoHD
Thinkbroadbamd Quality Monitors

burakkucat

  • Global Moderator
  • Senior Kitizen
  • *
  • Posts: 30804
  • Over the Rainbow Bridge
    • The ELRepo Project
Re: Fantasy future jumbo MRU / MTU
« Reply #12 on: October 15, 2020, 12:15:25 AM »

Can you translate it for us dumb humans? 

The document I found and downloaded (802.1AB Overview Link Layer Discovery Protocol - IEEE 802) turned out to be a set of slides from a presentation to the IEEE 802.3 Frame Expansion Study Group, at Ottawa, on Sept 30, 2004. The Wikipedia page, Link Layer Discovery Protocol, is obviously more current.

Essentially, it is a unified method to discover accessible devices at the link layer (of the OSI seven layer model) designed to supersede various proprietary protocols.

I think CarlT would be the best person to explain it in any detail.
Logged
:cat:  100% Linux and, previously, Unix. Co-founder of the ELRepo Project.

Please consider making a donation to support the running of this site.

Weaver

  • Addicted Kitizen
  • *****
  • Posts: 9114
  • Retd sw dev; A&A; 4 × 7km ADSL2; IPv6; Firebrick
Re: Fantasy future jumbo MRU / MTU
« Reply #13 on: October 15, 2020, 08:31:24 PM »

My HP switch has support for LLDP and LLDP-MED.
Logged