I need someone to explain to me how the IPv6 addresses are assigned and treated as primary/secondary. Is it the same as it was with IPv4 - single primary, multiple secondaries or not.Is there an hierarchy among the IPv6 addresses assigned or it is a flat list.
Thanks!
It is a flat list. All other things like common prefix length equal and with no temporary (privacy) addresses Linux will usually use the last added static address as the default source address. You can override this by setting a specific src address on the default route:
ip -6 route add default via 2001:db8::1 dev ethic src 2001:db8::abcd
Related
A listing in one of Azure networks reveals following address space ace::/64
What it is?
It's the short form for an IPv6 address. The extended form would be ace:0:0:0:0:0:0:0, however, blocks with 0 can be shortened with the double colon, so the result is ace::. The /64 means, that the address block marked by this address contains 2^64 addresses (an IPv6 address has 128 bits, and in this case 64 bits describe the network, and the other 64 can be assigned to actual devices in the network).
When I use this utility with nodejs: https://nodejs.org/api/dns.html#dns_dns_reverse_ip_callback
like so:
const {remoteAddress, remotePort} = req.connection;
dns.reverse(remoteAddress, (err, hostnames) => {
if(err){
console.error(err.message);
}
});
I get that error -
getHostByAddr ENOTFOUND ::ffff:18.234.32.226
what is the ffff stuff at the beginning of the address/ip? I assume I should get rid of that before passing to the dns.reverse lookup call?
::ffff:18.234.32.226 is an IPv4 address (18.234.32.226) mapped as an IPv6 one, which you detect because of the use of :.
This is a common case that happens on systems configured to prefer IPv6 over IPv4 (something you can configure in Unix systems with the file /etc/gai.conf).
It is explained in https://www.rfc-editor.org/rfc/rfc3493 section 3.7:
The API also provides a different type of compatibility: the ability
for IPv6 applications to interoperate with IPv4 applications. This
feature uses the IPv4-mapped IPv6 address format defined in the IPv6
addressing architecture specification [2]. This address format
allows the IPv4 address of an IPv4 node to be represented as an IPv6
address. The IPv4 address is encoded into the low-order 32 bits of
the IPv6 address, and the high-order 96 bits hold the fixed prefix
0:0:0:0:0:FFFF. IPv4-mapped addresses are written as follows:
::FFFF:<IPv4-address>
You need either to configure your system not to map IPv4 addresses as IPv6 ones, or use a library that knows how to handle those IP addresses (which are completely legit). Or in the worse case, indeed remove yourself the ::ffff: at beginning.
I'm facing for the first time with the new name scheme of network interfaces: Predictable Network Interface Name.
My question is NOT related if this scheme is better or worse... I'm just trying to understand how to use it correcly.
Here I read:
When changing the interface naming scheme, do not forget to update all network-related configuration files and custom systemd unit files to reflect the change.
So I have to write in all the configuration files the actual interface name. In the previous scheme it was i.e. eth0 and it just means the first ethernet card, with the known caveats if there are multiple interfaces.
Now, instead, I have to write the predictable name, that is composed of some easy parts (i.e. type of the interface) and other un-predictable ones like the MAC address. As far as I understand each card will have a different name.
I admit my question might appear fool, but I don't understand how to prepare a configuration file. Let's see an example, /etc/dhcpcd.conf:
profile static_eth0
static ip_address=192.168.1.23/24
static routers=192.168.1.1
static domain_name_servers=192.168.1.1
interface eth0
fallback static_eth0
What should I put instead of eth0 in the o.s. image?
Only when I run the target machine I can retreive the actual name of the ethernet interface.
100% of my systems are headless, and I never connect a keyboard and display to them. Furthermore, if I have to send a spare part of the SBC do I need to reconfigure all?
Would you please help me to understand the correct usage?
ps. I know I can revert back to the old naming scheme... but that's not the point of my question.
See https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/
it explains how the names are assigned
Names incorporating Firmware/BIOS provided index numbers for on-board devices (example: eno1)
Names incorporating Firmware/BIOS provided PCI Express hotplug slot index numbers (example: ens1)
Names incorporating physical/geographical location of the connector of the hardware (example: enp2s0)
Names incorporating the interfaces's MAC address (example: enx78e7d1ea46da)
Classic, unpredictable kernel-native ethX naming (example: eth0)
By default, systemd v197 will now name interfaces following policy 1) if that
information from the firmware is applicable and available, falling back to 2) if
that information from the firmware is applicable and available, falling back to 3)
if applicable, falling back to 5) in all other cases. Policy 4) is not used by
default, but is available if the user chooses so.
So you could opt for a different approach, likely in your setup its easiest to take the mac, just reboot once an image that tries pxe/dhcp requests and note down the sended mac.
Another way, that may work, depending on your setup, would be interface groupings.
From "man interfaces"
auto /eth*
If the kernel knows about the interfaces with names lo, eth0 and eth1, then the above line is then interpreted as:
auto eth0 eth1
Note that there must still be valid "iface" stanzas for each matching interface. However, it is possible to combine a pattern with a mapping to a logical interface, like so:
auto /eth*=eth
iface eth inet dhcp
So maybe if you only have one interface, but can't tell where it will be assigned, you could write "auto /e*=eth" to catch all interfaces starting with e and address them inside the configuration file as "eth".
I want to check if an IP address belongs to a subnet. The pain comes when I must check against 300.000 CIDR blocks having subnets ranging from /3 to /31, several million times / second.
Take https://github.com/indutny/node-ip for example:
I could ip.cidrSubnet('ip/subnet') for each all of the 300.000 blocks and check if the IP I'm looking for is inside the first-last address range, but this is very costly.
How can I optimally check if an IP address belongs to one of these blocks, without looping everytime through all of them?
Store the information in a binary tree that is optimized for range checks.
One naive way to do it is to turn each CIDR block into a pair of events, one when you enter the block, one when you exit the block. Then sort the list of events by IP address. Run through it and create a sorted array of IP addresses and how many blocks you are in. For 300,000 CIDR blocks there will be 600,000 events, and your search will be 19-20 lookups.
Now you can do a binary search of that file to find the last transition before your current IP address, and return true/false depending on whether that was in one or more blocks versus in none.
The lookup will be faster if instead of searching a file, you are searching a dedicated index of some sort. (The number of lookups in the search is the same or slightly higher, but you make better use of CPU caches.) I personally have used BerkeleyDB's BTree data structure for this kind of thing in other languages, and have been very happy.
If you have a IPv6 enabled host that has more than one global-scope address, how can you programmatically identify the preferred address for bind()?
Example address list:
eth0 Link encap:Ethernet HWaddr 00:14:5e:bd:6d:da
inet addr:10.6.28.31 Bcast:10.6.28.255 Mask:255.255.255.0
inet6 addr: 2002:dce8:d28e:0:214:5eff:febd:6dda/64 Scope:Global
inet6 addr: fe80::214:5eff:febd:6dda/64 Scope:Link
inet6 addr: 2002:dce8:d28e::31/64 Scope:Global
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
On Solaris you can indicate a preferred address with an interface flag and it is available programmatically via SIOCGLIFCONF:
/usr/include/net/if.h:
#define IFF_PREFERRED 0x0400000000 /* Prefer as source address */
As listed in the interface list:
eri0: flags=2104841<UP,RUNNING,MULTICAST,DHCP,ROUTER,IPv6> mtu 1500 index 2
inet6 fe80::203:baff:fe4e:6cc8/10
eri0:1: flags=402100841<UP,RUNNING,MULTICAST,ROUTER,IPv6,PREFERRED> mtu 1500 index 2
inet6 2002:dce8:d28e::36/64
This is not portable to OSX, Linux, FreeBSD, or Windows though. Windows is let off easy though as it has completely useless, from an administrators perspective, UUID based adapter names (depending upon the Windows version).
For Linux this article details how the parameter preferred_lft, where lft is short for "lifetime", can be altered to weight the selection process by the kernel. This setting doesn't appear conveniently available in the results of SIOCGIFCONF or getifaddrs() though.
So I want to bind to eth0, eri0, or whatever available interface name. The choices are a bit stark:
Fail on adapter names resolving to multiple interfaces. I take this approach for handling multicast transports (OpenPGM) as the protocol MUST have one-only sending address.
Bind to everything. This is a cop out and would be unexpected to users.
Bind to the adapter with SO_BINDTODEVICE. This requires CAP_NET_RAW system capability on Linux which can be quite a cumbersome overhead for administrators.
Bind to the first IPv6 interface on the adapter. The ordering tends to be completely bogus.
Bind to the last interface. David Croft's article implies Linux does this, but is also a bit bogus.
Enumerate over every interface and create a new socket explicitly for each.
With option #6 I would expect you could usually be smarter and take the approach that if only a link-local scope address is available bind to that, otherwise bind to just the available global-link scope addresses.
When connecting to another host then RFC 3484 can be used, but as you can see all the choices are dependent upon matching the destination address:
Prefer same address. (i.e. destination is local machine)
Prefer appropriate scope. (i.e. smallest scope shared with the destination)
Avoid deprecated addresses.
Prefer home addresses. Prefer outgoing
interface. (i.e. prefer an address on the interface we're sending
out of)
Prefer matching label.
Prefer public addresses.
Use longest matching prefix.
In some circumstances we can use #7 here, but in the interface example above both global-scope interfaces have a 64-bit prefix length.
RFC 3484 has the following pertinent lines:
The IPv6 addressing architecture 5 allows multiple unicast
addresses to be assigned to interfaces. These addresses may have
different reachability scopes (link-local, site-local, or global).
These addresses may also be "preferred" or "deprecated" 6.
The link being to RFC 2462, similarly expanded:
preferred address - an address assigned to an interface whose use
by
upper layer protocols is unrestricted. Preferred addresses may
be used as the source (or destination) address of packets sent
from (or to) the interface.
But no methods to programmatically acquire this detail.
Props to Win32 API that exposes an ioctl SIO_ADDRESS_LIST_SORT that allows a developer to use not only RFC 3484 sorting but to take into consideration any system administrator overrides. Linux has /etc/gai.conf as used for RFC 3484 sorting in getaddrinfo() but no API for directly accessing the sorting. Solaris has the ipaddrsel command. OSX is following FreeBSD by adding ip6addrctl in 10.7.
edit: Some concerns with RFC 3484 sorting are listed and referred to in this additional IETF draft document:
https://datatracker.ietf.org/doc/html/draft-axu-addr-sel-01
Solaris, for example, creates new alias-interfaces for each new
address assigned to a physical interface. So if_index could also be
used to uniquely identify a source address specific routing table on
that platform. Other operating systems do not work the same way.
The author likes Solaris's approach of giving each additional IPv6 interface a new alias, so that eri0 would become the link-local scope address, and eri0:1 or eri0:2, etc, must be specified to use a global-scope address.
Clearly whilst a nice idea one couldn't expect to see other OS change for quite some time.
I'm not sure this is in the direction you're seeking, but...
Poking around in the iproute bundle's ip code (ip/ipaddress.c) under linux shows that the ip command digs up interface flags like primary and secondary from a struct ifaddrmsg, member ifa_flags. The ifaddmsg seems to be acquired through a struct nlmsghdr which is documented in man 7 netlink, and used via sendmsg and recvmsg interaction with the kernel, which overall sounds like a royal pain but it's at least programmatic. Whether primary and secondary would be enough to be useful is a separate question.