I've seen around IPv4 subnet address ranges expressed in a compact form.
For example:
127/24 == 127.0.0.0/24
10/8 == 10.0.0.0/8
10.10.10/24 == 10.10.10.0/24
BTW I can't find any RFC (or any other kind of official or semi-official documentation) that describes it.
Does anyone have some links to share?
I recall this notation being used on Juniper routers as far back as 2001; not sure what, if any, RFC defined it. RFCs do not define the whole planet; somehow over the years they replaced specifications (which are/were much more detailed), but were originally intended for Request For Comments. (Gee, I wonder why there are so many bugs in networking gear.)
Related
There're simple structures of network protocols (e.g. ipv4, tcp, udp, ...) which can be can be easily described in any language via strictures. But there are more difficult structures with optional fields/block and dynamic block/field sizes (TVL, LT, etc.) - e.g. ipv6, sctp, PROFINET-IO (decentralized periphery), ...
My question is - How to properly describe the protocol data structure and store that for future using? E.g. generating structures for different languages, or getting all trees (e.g. in ipv6 Wireshark ipv6.opt.pdm.delta_last_recv), or getting all fields for specific block/extension/option of the protocol.
I hope the description is clear. Thanks.
The ASN1 language was created to solve this and other problems like it. IMHO, the reason that you do not see it used often is that the language got very complex and different factions started to use it in different ways (SNMP MIBs, Crypto X509, etc) which resulted in ASN1 compilers being specialized and not general.
Often instead of ASN1 you see a C-Struct definition of the packet or just an RFC packet diagram ( you can use the protocol tool to generate one) with some markings (like ...) to indicate variable length.
I guess protobuf technically also qualifies as a language that describes a binary message though I do not believe it is a general language that can describe any message and is meant to be used by other protobuf-enabled applications.
I took a look over the already asked questions and I didn't find the information I need. In case I miss the questions somehow, please accept my apologize.
I would like to know how can I use a router as switch on GNS3? Since GNS3 (at least in this moment) doesn't accept switches images, how can it be done?
Once this step is made, it is possible to use most the important switch functions? like etherchannel, trunk, multiple vlans etc.
Thank you very much.
Firstly, there is no true way to put switching into hardware, as of yet, that is. The TCAM's functions in L3 switches these days has yet to be perfected in software.
Secondly, there are a couple of ways to do this, but out of the three, two of them will either cost money or take some investigative work.
Drag the switch icon into the simulation. You can do vlan tagging as an access port, or as a trunk port. No etherchannel though. Alternatively, the 3725 Router has some switching capabilities using the 16-ESW card, however functionality is limited and syntax differs.
Buy VIRL from Cisco's website. It is basically an Ubuntu VM with Cisco routers, IOSvL2 (a switch essentially), ASAv, and a couple other virtual network devices. However, if you're not a student, it's a few bucks. In addition, it is subscription based
3.Upload IOU to GNS3. You will need:
-IOU image, found here: http://sourceforge.net/projects/gns-3/files/IOU%20VMs/
-Virtualbox
-License file for IOU
-GNS3 (Obviously)
-L2/L3 IOU images (The L2 images are switches)
You can find the instructions here: http://srijit.com/how-to-configure-iou-in-gns3-for-real-cisco-switching-labs/
Hope this helps.
In RFC 5952 - section 5 it is stated that for some IPv6 addresses it is recommended to give the mixed notation, if it has a certain prefix. However, it is unclear which prefixes are used for this, because it is stated that a prefix may be used if it is commonly used as a prefix for a IPv4-mapped address. Thus meaning basically any prefix could be used for this.
Now my question is:
May every IPv6 address be written as an IPv4-mapped IPv6-address?
If not, what are the exact rules for correctly writing an IPv4-mapped IPv6-address?
You may use the IPv4 notation for the last 32 bits in any IPv6 address. The RFC you mention is about the recommended notation. It doesn't specify all correct notations. The RFC that defines that is https://www.rfc-editor.org/rfc/rfc4291#section-2.2 and it allows the IPv4 style notation (Note that it isn't called "IPv4-mapped IPv6-address", that is actually a special range of addresses that commonly used this notation style) for any address.
I'm being asked to determine whether this dig answer is authoritative or not.
I'd say yes, but I am not too keen on that.
The rationale behind believing it is indeed authoritative is that the AUTHORITATIVE SECTION contains two addresses, that from what one can see from the ADDITIONAL SECTION map to 194.117.22.138 and 10.101.85.6.
We know that this answer was replied from 194.117.22.138, so it must be the case that the server is authoritative.
Is my reasoning correct or am I taking the wrong approach here?
Please see DNS response flags on the third line of dig output. There is a flag named aa which means "authoritative answer".
I think there are a lot of people out there unaware of RFC's (Request for Comments). I know what they are at a logical level, but can anybody give a good description for a new developer? Also, sharing some resources on how to use and read them would be nice.
The term comes from the days of ARPANET, the predecessor to the internet, where the researchers would basically just throw ideas out there to, well, make a request for comments from the other researchers on the project. They could be about pretty much anything and were not very formal at the time. If you go read them, it’s pretty comical how informal they were.
Now, there are more standards about what goes in RFC's and you can't get an RFC published until you have met strict guidelines and have done extensive research. They are pretty much reserved for well researched network standards that have been approved by the IETF.
From http://linux.about.com/cs/linux101/g/rfclparrequestf.htm
The name of the result and the process
for creating a standard on the
Internet. New standards are proposed
and published on the Internet, as a
Request For Comments. The proposal is
reviewed by the Internet Engineering
Task Force (http://www.ietf.org/), a
consensus-building body that
facilitates discussion, and eventually
a new standard is established, but the
reference number/name for the standard
retains the acronym RFC, e.g. the
official standard for e-mail message
formats is RFC 822.
See also: RFC Wikipedia Article
This could also mean "Request for Change" in an Agile environment. Just throwing that out there as everyone is so certain is just means "Request for Comments".
Wikipedia gives a good description of what [RFC] is about but in a nutshell it is a set of recommendation from the Internet Engineering Task Force applicable to the working of the Internet and Internet-connected systems. They are used as the standards.
So if you're looking for a definitive source of the information about the implementation of FTP, LDAP, IMAP, POP etc you don't have to look further than the appropriate RFC documents.
It's a Request For Comments. That title is a little misleading though, as it's often used as a name for standards, mostly those by the IETF. See Wikipedia