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I have a fundamental question with respect to iptables processing logic.
I see iptables have chains PREROUTING, INPUT, OUTPUT, FORWARD and POSTROUTING. And these chains are present in multiple tables.
Based on what I have understood so far, the packet arrives into PREROUTING, then based on routing rules if the packet is meant for the local machine enters INPUT chain. Else it goes to FORWARD chain and then later on POSTROUTING.
But my fundamental question is, if there are multiple INPUT rules in multiple tables. In what order are the tables processed in ? I read that the first table would be raw. But what about the rest ?
Thanks !
For understanding the traversing of each table please go through this guide it would help you understand the flow http://www.faqs.org/docs/iptables/traversingoftables.html
INPUT chains are used only in Filter and Mangle table(used for alteration of packets)
Thanks & Regards,
Alok
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Closed 1 year ago.
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I used CuteCom tool to parse the GNSS receiver data in Ubuntu Desktop 20.04 LTS. In the case of not receiving satellite signals, it can generate normal data. But when I went outside to receive the signal, it generated some message except NMEA sentence. Like this:
I don't know what made this. Who can help me? Thanks in advance.
Maybe I have found why CuteCom displayed additional data. That's because the receiver will output Raw data besides NMEA sentences.
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Closed 4 years ago.
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I came across a rule:
iptables -A INPUT -p tcp -s 17.3.3.5/24 -d 0/0 --dport 22 -j DROP
and I was just wondering if someone could explain what this rule is doing. More importantly, I would like to know what the
-d 0/0
part means, in the whole rule (I know its destination specification, so the 0/0 part should be an IP address, but why is it 0/0?).
Im speculating that the rule is dropping that one source address when it arrives at destination port 22, but I'm not sure.
If someone could explain, that would be great.
Couldn't find an answer when searching the interwebs :C
Just like -s 17.3.3.5/24 means any source within the CIDR block 17.3.3.5/24, -d 0/0 means any destination within the CIDR block 0.0.0.0/0. Since there are no bits in the network number, every address is inside this network. So it means any destination at all.
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Closed 5 years ago.
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Just wondering what breaks the ties amount rows for a routing table. Thank you in advance for the help!
Administrative distance will be used by the routing table as the tie-breaker for candidate routes offered by the routing protocols.
when using the metric value to break a tie between entries in a routing table, the router selects the matching row with the highest or the lowest metric value, since the lower the value the more trusted the source of information is going to be.
That being said there are two parameters a router uses to break the tie;
Administrative Distance
Metric
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Closed 4 years ago.
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Problem, step by step:
Create a spreadsheet
Paste a csv file
Create a sort filter
Use the sort filter (A-Z)
Close the file (wait saving process)
Open the file (BANG: some rows was erased)
I consider a serious problem (consistency) as well as the correction a determining factor for an effective use or contracting of the solution.
This problem reproduced by me: https://youtu.be/M6_sEu8_F_E
Is there any expecting for repair or an alternative solution?
This problem will fixed in version 4.2
See https://github.com/ONLYOFFICE/DocumentServer/issues/63#issuecomment-259364585 (I assume this is your issue too)
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Closed 3 years ago.
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I'm interested in saving a pcap that has network layer name resolution. While it works great within Wireshark, how can I save it with the resolved names intact? Having this information would be extremely helpful for me and save me a lot of time if this is possible. I understand in the documentation that it can't be saved within the pcap file (http://www.wireshark.org/docs/wsug_html_chunked/ChAdvNameResolutionSection.html#idp390072124) but is there an alternative way to do so? Does anyone have any solutions to this?
Thanks in advance!
I haven't tried it myself, but in theory the name resolution information can/will be stored in the pcap-ng file format, which has been Wireshark's default file format since version 1.8. The old pcap file format you cite won't, but pcap-ng has a specific defined block type in its format for ip<->name resolution information.