Networking

Networking features are nowadays important for virtually all users of Fedora and other linux distributions. Fedora's main network use cases are laptops, desktops, servers and virtualization. Fedora could also be used for routers, becoming part of networking infrastructure.

Networking concepts and configuration

• Ethernet
• Addressing
• Routing
• Bridging
• Bonding / Teaming
• TCP, UDP and ICMP NAT
• Traffic control
• Tunneling
• Name Resolution
• Network connectivity dependencies

Most prominent projects involved in linux networking

• Kernel
• GLIBC
• NetworkManager
• ISC DHCP

Notable networking problems

Only platform bugs that can influence various application and/or the overall behavior of the system belong here.

Kernel

• Bridge: Adding first interface after setting MAC address changes the MAC address
• IPv4: Kernel can't store DHCP lifetime and cannot mark IPv6 addresses dynamic (in the DHCP sense)
• IPv6: Kernel ignores RA router preference
• IPv6: Tempaddr cycling breaks TCP connections prematurely
• IPv6: Kernel doesn't cache RDNSS and DNSSL
• IPv6: Kernel doesn't provide default route information when defrtr is disabled
• IPv6: Kernel doesn't provide prefix route information when pinfo is disabled

libnl

• rtnl_link_bond_add() succeeds when device already exists
• rtnl_link_bridge_add() and rtnl_link_vlan_add missing

iproute

• iproute won't distinguish bridges and bonds
• iproute won't show vlan id

GLIBC

• IPv4: getaddrinfo(127.0.0.1, AI_ADDRCONFIG) fails on hosts without global IPv4 (e.g. notebooks not connected to any networks)
• IPv6: getaddrinfo(::1, AI_ADDRCONFIG) fails on hosts without any other IPv6 address
• IPv6: getaddrinfo(link-local-address, AI_ADDRCONFIG) fails on hosts without global IPv6 (hopefully solved)
• IPv6: GLIBC's nsswitch doesn't support overriding getaddrinfo which is requred to resolve link-local IPv6 addresses
• DNS: getaddrinfo doesn't support SRV records

More information about AI_ADDRCONFIG problems

dhclient

• Fixed: dhclient fails with large values of dhcp-renawal-time, notably the infinity (0xffffffff) value
• People say that dhclient exchange is slow, especially on wireless (I can't reproduce)

Avahi

• Avahi's nss-mdns returns link-local IPv6 addresses without scope_id and applications fail to connect
• Avahi's IPv6 support is disabled by default (this has been resolved in the past)

NetworkManager

• Various bugs in NetworkManager

Testing tools

• ping doesn't support IPv6 (you have to use ping6)
• netstat and ss won't mark non-v6only sockets

Various applications

• Assume that getaddrinfo() returns only one address and/or that such the first returned address works. See Networking/NameResolution.

Network related standards

• RFC 6106 (RA DNS): Relies on a false assuption that every (even multicast) IP packet is delivered to its destination.
• RFC 4861 (NDP): Doesn't specify how zero lifetimes should be used and lets implementations rely on the same false assumption.
• RFC 3493 (socket interfce): Breaks both IPv4 and IPv6 localhost and link-local networking depending on available global addresses.
• POSIX.1-2008: Defines the AI_ADDRCONFIG in a bad way

Peaces of the puzzle

• Interface for static IPv4 and IPv6 configuration (kernel)
• Interface for bridging/bonding/vlan configuration (kernel)
• Interface for DNS configuration (/etc/resolv.conf)
• DHCP client implementation for IPv4 automatic configuration (dhclient)
• RA client implementation for IPv6 address configuration (kernel, with workarounds in NetworkManager)
• RDNSS/DNSSL client implementation for IPv6 DNS configuration (NetworkManager through kernel, with workarounds)
• DHCP client implementation for IPv6 address/DNS/other configuration (dhclient)
• IPsec, VPN and tunneling implementations (various daemons)
• A network management daemon to properly manage all of the above together with user configuration (NetworkManager)
• Networking API for applications (glibc, with many problems)

I may have missed something but the objective is to show that networking is rather complex and the various tools need to be centrally managed by a network management service in order to make users and administrators happy.

You can only live without network configuration daemons if you use static IP configuration and you avoid encrypted wireless networks at the same time. You can live with just wpa_supplicant and dhclient only if you are used to do most of the stuff yourself. Virtually all linux distributions now converge to network solutions based on network configuration daemons.

Examples of such daemons (without feature comparison):

• NetworkManager
• connman (MeeGo)
• WICD
• netifd (OpenWRT)
• netcfg (Archlinux)
• wicked

Yeah, it's a lot of fun writing new and new network configuration daemons.

Features to be proposed at some point of time

• Features/DualstackNetworking
• Features/ZeroconfNetworking
• Features/NetworkManagerBonding
• Features/NetworkManagerBridging
• Features/NetworkManagerAdvancedIPv6
• Features/NetworkManagerCLIAddConnection

Contacts

Name: Pavel Šimerda Email: psimerda@redhat.com IRC: pavlix, #nm at freenode

Use the above contacts or Talk:Networking for discussions about Networking page, its subpages, related pages and covered topics. Add yourself to the contacts if you want to help me maintaining this set of information resources.