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Diffstat (limited to 'Documentation/networking/operstates.txt')
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diff --git a/Documentation/networking/operstates.txt b/Documentation/networking/operstates.txt deleted file mode 100644 index b203d1334822..000000000000 --- a/Documentation/networking/operstates.txt +++ /dev/null @@ -1,164 +0,0 @@ - -1. Introduction - -Linux distinguishes between administrative and operational state of an -interface. Administrative state is the result of "ip link set dev -<dev> up or down" and reflects whether the administrator wants to use -the device for traffic. - -However, an interface is not usable just because the admin enabled it -- ethernet requires to be plugged into the switch and, depending on -a site's networking policy and configuration, an 802.1X authentication -to be performed before user data can be transferred. Operational state -shows the ability of an interface to transmit this user data. - -Thanks to 802.1X, userspace must be granted the possibility to -influence operational state. To accommodate this, operational state is -split into two parts: Two flags that can be set by the driver only, and -a RFC2863 compatible state that is derived from these flags, a policy, -and changeable from userspace under certain rules. - - -2. Querying from userspace - -Both admin and operational state can be queried via the netlink -operation RTM_GETLINK. It is also possible to subscribe to RTNLGRP_LINK -to be notified of updates while the interface is admin up. This is -important for setting from userspace. - -These values contain interface state: - -ifinfomsg::if_flags & IFF_UP: - Interface is admin up -ifinfomsg::if_flags & IFF_RUNNING: - Interface is in RFC2863 operational state UP or UNKNOWN. This is for - backward compatibility, routing daemons, dhcp clients can use this - flag to determine whether they should use the interface. -ifinfomsg::if_flags & IFF_LOWER_UP: - Driver has signaled netif_carrier_on() -ifinfomsg::if_flags & IFF_DORMANT: - Driver has signaled netif_dormant_on() - -TLV IFLA_OPERSTATE - -contains RFC2863 state of the interface in numeric representation: - -IF_OPER_UNKNOWN (0): - Interface is in unknown state, neither driver nor userspace has set - operational state. Interface must be considered for user data as - setting operational state has not been implemented in every driver. -IF_OPER_NOTPRESENT (1): - Unused in current kernel (notpresent interfaces normally disappear), - just a numerical placeholder. -IF_OPER_DOWN (2): - Interface is unable to transfer data on L1, f.e. ethernet is not - plugged or interface is ADMIN down. -IF_OPER_LOWERLAYERDOWN (3): - Interfaces stacked on an interface that is IF_OPER_DOWN show this - state (f.e. VLAN). -IF_OPER_TESTING (4): - Unused in current kernel. -IF_OPER_DORMANT (5): - Interface is L1 up, but waiting for an external event, f.e. for a - protocol to establish. (802.1X) -IF_OPER_UP (6): - Interface is operational up and can be used. - -This TLV can also be queried via sysfs. - -TLV IFLA_LINKMODE - -contains link policy. This is needed for userspace interaction -described below. - -This TLV can also be queried via sysfs. - - -3. Kernel driver API - -Kernel drivers have access to two flags that map to IFF_LOWER_UP and -IFF_DORMANT. These flags can be set from everywhere, even from -interrupts. It is guaranteed that only the driver has write access, -however, if different layers of the driver manipulate the same flag, -the driver has to provide the synchronisation needed. - -__LINK_STATE_NOCARRIER, maps to !IFF_LOWER_UP: - -The driver uses netif_carrier_on() to clear and netif_carrier_off() to -set this flag. On netif_carrier_off(), the scheduler stops sending -packets. The name 'carrier' and the inversion are historical, think of -it as lower layer. - -Note that for certain kind of soft-devices, which are not managing any -real hardware, it is possible to set this bit from userspace. One -should use TVL IFLA_CARRIER to do so. - -netif_carrier_ok() can be used to query that bit. - -__LINK_STATE_DORMANT, maps to IFF_DORMANT: - -Set by the driver to express that the device cannot yet be used -because some driver controlled protocol establishment has to -complete. Corresponding functions are netif_dormant_on() to set the -flag, netif_dormant_off() to clear it and netif_dormant() to query. - -On device allocation, both flags __LINK_STATE_NOCARRIER and -__LINK_STATE_DORMANT are cleared, so the effective state is equivalent -to netif_carrier_ok() and !netif_dormant(). - - -Whenever the driver CHANGES one of these flags, a workqueue event is -scheduled to translate the flag combination to IFLA_OPERSTATE as -follows: - -!netif_carrier_ok(): - IF_OPER_LOWERLAYERDOWN if the interface is stacked, IF_OPER_DOWN - otherwise. Kernel can recognise stacked interfaces because their - ifindex != iflink. - -netif_carrier_ok() && netif_dormant(): - IF_OPER_DORMANT - -netif_carrier_ok() && !netif_dormant(): - IF_OPER_UP if userspace interaction is disabled. Otherwise - IF_OPER_DORMANT with the possibility for userspace to initiate the - IF_OPER_UP transition afterwards. - - -4. Setting from userspace - -Applications have to use the netlink interface to influence the -RFC2863 operational state of an interface. Setting IFLA_LINKMODE to 1 -via RTM_SETLINK instructs the kernel that an interface should go to -IF_OPER_DORMANT instead of IF_OPER_UP when the combination -netif_carrier_ok() && !netif_dormant() is set by the -driver. Afterwards, the userspace application can set IFLA_OPERSTATE -to IF_OPER_DORMANT or IF_OPER_UP as long as the driver does not set -netif_carrier_off() or netif_dormant_on(). Changes made by userspace -are multicasted on the netlink group RTNLGRP_LINK. - -So basically a 802.1X supplicant interacts with the kernel like this: - --subscribe to RTNLGRP_LINK --set IFLA_LINKMODE to 1 via RTM_SETLINK --query RTM_GETLINK once to get initial state --if initial flags are not (IFF_LOWER_UP && !IFF_DORMANT), wait until - netlink multicast signals this state --do 802.1X, eventually abort if flags go down again --send RTM_SETLINK to set operstate to IF_OPER_UP if authentication - succeeds, IF_OPER_DORMANT otherwise --see how operstate and IFF_RUNNING is echoed via netlink multicast --set interface back to IF_OPER_DORMANT if 802.1X reauthentication - fails --restart if kernel changes IFF_LOWER_UP or IFF_DORMANT flag - -if supplicant goes down, bring back IFLA_LINKMODE to 0 and -IFLA_OPERSTATE to a sane value. - -A routing daemon or dhcp client just needs to care for IFF_RUNNING or -waiting for operstate to go IF_OPER_UP/IF_OPER_UNKNOWN before -considering the interface / querying a DHCP address. - - -For technical questions and/or comments please e-mail to Stefan Rompf -(stefan at loplof.de). |