3,961 reputation
917
bio website
location London, United Kingdom
age 43
visits member for 5 years, 5 months
seen Oct 22 at 11:11
Quite boring, really. Have faffed about with computers since the mid-80s, have worked as a network engineer, unix sysadmin and (occasionally) developer.

Jul
30
comment What does mdev mean in ping(8)?
@dmourati Actually, no, the jitter is the difference between the lowest and highest RTT (or, equally, the difference from min to mean and teh difference from mean to max, depending on if you see it as "I ms" or "-A / +B ms".
Oct
17
comment Is anyone using GPS for time sync?
@ChrisS I've always interpreted the strata as being specifically only within NTP. But I am happy to change my understanding. Thank you.
Aug
31
comment How do I redirect output to a single line in Bash?
If at all possible, get in the habit of using $( ... ) instead of `...`. That way, it's easy to capture the output of a command taht uses captured output. If you use backticks, it's almost impossible.
Feb
28
comment Securing the network: IP conflicts and its solutions
MAC addresses are (typically) not randomly picked on boot.
Jan
5
comment Cable Management
I started out thinking zip ties were the perfect answer, but have eventually come around to the idea that zip ties are really good for infrequently-touched equipment racks. When you're in the rack, making modifications to the cabling (by installing, uninstalling and/or moving kit), velcro is a much better idea.
Dec
21
comment Is Selling Old Cisco Routers a Security Issue?
The RJ-45-contacted cable is a roll-over, so the pins are connected 1-8, 2-7, 3-6, 4-5. Trivial to make and there are RJ-45 couplers tha timplement a rollover, so you can just take two ethernet cables with the coupler in-between.
Nov
19
comment Regex working in RedHat is not giving any result in Ubuntu
I think you're using a glob rather than a regex...
Oct
31
comment linux + run some script without “./” + alias
The PATH variable should never point to individual binaries (or scripts), only to the directories they're contained within.
Oct
28
comment Is it possible that this email was sent when the sender claims?
@peter nixey: I'd prefer to not speculate on that. :) I've speculated on the possibility, but as far as "probability" and "plausibility", I'd really want to know the human actors good enough.
Oct
28
comment Is it possible that this email was sent when the sender claims?
If the problem was, say, "the DSL link was broken for several weeks" (or "unstable enough that it never completed sending the email"), possibly. The DSL situation in Britain is... interesting. There are usually multiple parties involved, the ISP providing the connection to the internet at large, the ex-monopoly telco (or another operator!) providing infrastructure to haul the traffic from the consumer to the ISP and (sometimes, but that is probably pretty rare) another provider of the last little bit of cable (more "the last few yards" than "the last mile").
Oct
26
comment cisco - enable port automatically if conn lost?
As an extra safety precaution, I tended to make a second (post-change) connection to the router, to issue the "reload cancel". That way I know that authentication still works.
Oct
25
comment running command with sudo gives different result
It's equally efficient to do something like: ps -aef | grep [x]inetd The square brackets around the x indicate 'match the character class that only has an x' so /[x]inetd/ match "xinetd" but not "[x]inetd".
Sep
1
comment How many computers can have the same public IP?
@Ian Boyd: The complete identifier for a TCP session is <src ip><src port><dst ip><dst port> and with sufficient state in the NAT table, you can share either src or dst port if the other one is different. It's not usually done that way, though (thus things like "cone-shaped NAT" working most of the time).
Aug
5
comment Is it normal to have a private range IP in a traceroute?
@womble: If you go for private IPs on you backbone links (something that used to be recommended, to preserve IPv4 space), you will want to leak a small subset of control packets from them (TTL exceeded, Fragmentation needed, possibly a few more).
Aug
1
comment cisco router : redirect any dns request to my own dns server
@qwildz: It probably varies from router to router, but enabling policy-routing tends to drop from CEF to slower forwarding algorithms. On low-end hardware, it tends to end up being CPU-switched.
Jul
31
comment Certificate Authority impersonation
@Zoredache: Typically, in a public-key cryptosystem, you have, for a message M and a key-pair P,S and two operation E,D that D(P,E(S,M)) == D(S, E(P, M)) == M; that is, encryption of a plain-text with one half of the key-pair, followed by decryption of the crypto-text with the other half of the key-pair results in the plain-text.
Jul
27
comment IPv4 address to Netmask mapping and Multiple default routes feasibility?
I think Linux will, by default, do round-robin load-balancing between default gateways with the same metric. In some situations, this is exactly what you want, in others it will break things horribly. Keeping to a single default gateway or having different metrics is definitely the safe bet.
Jul
26
comment Small office network labeling
Labeling each end of the cable with both pieces of kit it plugs into is a good idea, as long as you relabel the cable as soon as anything changes...
Jul
15
comment web page slow load due to long DNS lookup
How frequently do you need to change them? How long is it acceptable that a DNS lookup points to an old IP address after a change? How long in advance do you know that you will need to make a change? Once you have the answers to those questions, picking a number of seconds for the (default) TTL should be not-too-hard. I've seen TTLs in the region of 3600-86400 work fairly well (that allows a client to cache the lookup for 1h-1d) and if you know you have a change coming up, you can always push the TTL down to 600-or-so 1.5 (default) TTLs before you do the change.
Jul
1
comment Cisco ACL Not Applying
You can certainly apply a single ACL both in- and out-bound. I have done it multiple times. Admittedly prima=rily for "tracking" ACLs (with specific "ip permit" statements for what I am interested in, finishing with a blanket "ip permit any any")