1,797 reputation
815
bio website perlmonkey.blogspot.com
location United Kingdom
age 39
visits member for 5 years, 6 months
seen Oct 7 at 14:14

I have been working as a Network Engineer and Systems Administrator in ISP/Telecommunications networks since 1996. I have extensive experience the BGP, OSPF, MPLS, IPv6, VoIP, ATM, DSL, QoS and many other TLAs.

I am married with a son and three dogs. I enjoy skateboarding, cycling, reading, music and pondering on the future of networking.


Feb
21
comment What is the Maximum MTU supported in DSL Standards
A mostly correct answer, but not to the question asked. I am a little wary about resurrecting this 4 year old question, as I am no longer involved in DSL service provision; however MTU and large scale misunderstanding of it is still a personal hobby horse of mine. You are correct to state that 4470 is often used as a default when running IP over AAL5 on ATM; however it is a convention not a standard. My question is whether the ITU standards define a maximum MTU for DSL, not what common conventions are used.
Apr
26
comment How can I find out the next IPv6 address?
While I agree that trying to use stateless auto-config with less than a /64 is likely to cause a lot of pain, there is nothing in the RFCs that preclude the use of longer masks when manually configuring things. Auto-config is great for home / office client PCs; however in a hosted server or network infrastructure use of stateless auto-config is generally frowned upon and addresses will either be assigned manually or using a stateful config method (e.g. DHCPv6).
Sep
30
comment How can I find out the next IPv6 address?
Off by one error ;) 4294967296 (2^32) is the number of possible addresses in a /96; however the actual range is 0 - (2^32 - 1)
Sep
30
comment How can I find out the next IPv6 address?
As an aside - a /96 gives you as many addresses to play with as the entire IPv4 address space. You probably don't have to worry about efficient usage of the space - A VPS probably isn't going to need all of those addresses just for itself...
Sep
30
comment How can I find out the next IPv6 address?
Makes sense. Does the rest of my answer address your question?
Jul
6
comment What is the Maximum MTU supported in DSL Standards
I'm not sure how much experience you have of dealing with incumbent telcos but my past experience tends to say that if you ask them this sort of question then you will be lucky to get any answer at all ;) To be honest I agree with you, the 1500 limit is likely to be entirely arbitrary choice made by the carrier. The main reason I asked the question though was to understand if there are any protocol limits or equipment limits rather than arbitrary design choices.
Jul
6
comment What is the Maximum MTU supported in DSL Standards
Pretty much any incumbent telecoms company will do this, e.g. British Telecom, Deutsche Telecom, France Telecom. The delivery mechanism varies and can include direct connection to an end-to-end ATM PVC, or a dedicated IP port delivering PPP over L2TP (often over ethernet with an MTU in the 2k-9k range).
Jul
6
comment What is the Maximum MTU supported in DSL Standards
I know that sending packets of more than 1500 bytes across the public internet is uncommon; however I use a lot of DSL lines in VPN deployments which go nowhere near the public internet and am curious as to why the MTU is still restricted in this situation.
Apr
1
comment Are there any statistics on the number of networks using Ethernet Jumbo frames?
A lot of people have posted comments on situation where they use Jumbos locally but not on the WAN. Can anyone comment on this: Would you consider a WAN ethernet link to be broken if it only allowed for a 1500 byte MTU? It seems the consensus so far is no.
Dec
8
comment Why am I getting long TCP connect latency on connect in a LAN (over a cross!)?
The problem with comparing time deltas is that it's impossible to tell whether there is a big delay in one direction, or whether there is a smaller delay in both directions :(
Dec
7
comment DNS using CNAMEs breaks MX records?
This is a common question and has been asked many times before. See this link for an example: serverfault.com/questions/18000/…
Dec
7
comment Why does psql attempt to connect with a different username when run from a Perl script
Do you have anything set in the PG* environment variables or a ~/.psqlrc file? Are there any map entries in the pg_ident.conf file?
Aug
3
comment How to delete all hidden files and directories using Bash?
Be careful with that shorter version, it will give similar, but not identical results. It won't match names with two dots at the front (e.g. ".../" which is sometimes seen hiding rootkits, etc.)
Jul
29
comment Making hosted applications resilient to BGP failures
Be wary of providers that will "cough up" a /24 or /23 of address space based on how much you are spending rather than demonstrable need. Chances are they are breaking the rules that they agreed to when becoming an LIR. Provision of Provider Independant address space is out of your service provider's hands. AFAIK no RIRs will make a PI assignment based on invoice size...
Jul
24
comment What IP MTU sizes are seen in real networks
Previous comment should have read the IEEE have never standardised Jumbo frames. IETF have no remit to mess with the 802 standards...
Jul
24
comment What IP MTU sizes are seen in real networks
Jumbo frames of 9k are quite common in datacentres, especially if there are NAS devices present. Some ethernet vendors support jumbos of higher than 9k (largest I have seen supported is 15k) but 9k is the largest that is likely to be seen cross-vendor. Even the 9k figure varies from vendor to vendor (e.g. 9000, 9192, 9600). The sizes vary from vendor to vendor due to the fact that the IETF have never standardised Jumbo frames. The 802.3 standards all give 1500 as the largest supported payload.
Jul
20
comment Do entries in local 'hosts' files override both forward and reverse name lookups?
I haven't had a chance to look at the source yet; however a quick look at ldd output shows that on my system ping is linked directly to the libresolv DNS resolver library, which could imply that it is bypassing the nsswitch file and doing its reverse lookups directly...
Jun
19
comment How does autodiscovery work?
I have updated my answer with information on where I have seen supplimenting SNMP with CDP to be useful.
Jun
19
comment How does autodiscovery work?
I don't think I suggested that it could in my answer. My intention was to state that protocols such as CDP and LLDP can allow a discovery application to gather more information about network topology. I have used several network discovery tools which make use of CDP information when walking the network.
Jun
17
comment How exactly do name servers handle unknown subdomains?
+1 for Princess Bride reference ;)