nexthop_group

Nexthop groups are a forwarding/tunneling abstraction in EOS.

A nexthop group is comprised of a tunneling protocol (IP/GRE or MPLS, for example) and a collection of nexthop (aka destination) IP addresses and other forwarding information (such as MPLS stack operations to apply for traffic sent to that nexthop). The same IP address may be specified in more than one entry within the group, allowing for unequal cost load balancing. By using distinct addresses for each entry, equal cost load balancing can be achieved.

The nexthop or destination IP is the tunnel (outer) destination IP address for GRE and IP-in-IP. For MPLS, the nexthop address is used to find (via ARP/ND) a MAC address for the MPLS next hop.

Nexthop entries must be manually monitored and maintained by the agent. If a tunnel destination (aka nexthop) becomes unreachable, traffic hashed to that entry will be black-holed in the network until a working entry is set in that index of the nexthop group, or the entry is deleted.

Presently, all nexthop groups encapsulate traffic directed to them, either as an IP-in-IP (IP protocol 4) tunnel, a GRE (IP protocol 47) tunnel encapsulating either IPv4, IPv6 or MPLS traffic, or as pure MPLS frames. MPLS label switching operations are also supported, see the nexthop_group_entry_t class for more information.

Presently, MPLS switching actions are only only supported when used with PBR and cannot be used with IP routes.

The following example creates a nexthop group called “nhg1” which performs GRE encapsulation of traffic sent to it, sending traffic to two different nexthop IP addresses unequally (at a 2/3 to 1/3 ratio). For a usage of a nexthop group with policy routing, see the policy_map.h file.

   eos::nexthop_group_t nhg("nhg1", eos::NEXTHOP_GROUP_GRE);
   // Specify two destinations (nexthop group entries) for the traffic
   eos::nexthop_group_entry_t nhe1(eos::ip_addr_t("172.12.1.1"));
   eos::nexthop_group_entry_t nhe2(eos::ip_addr_t("172.12.1.2"));
   // Set the nexthop group entries on the group with unequal cost load balancing
   // Balance traffic 2/3 to 172.12.1.1, 1/3 to 172.12.1.2.
   nhg.nexthop_set(0, nhe1);
   nhg.nexthop_set(1, nhe1);
   nhg.nexthop_set(2, nhe2);

namespace eos

class nexthop_group_handler

#include <nexthop_group.h>

This class handles changes to a nexthop group’s status.

Public Functions

nexthop_group_handler(nexthop_group_mgr *)

nexthop_group_mgr * get_nexthop_group_mgr() const

void watch_all_nexthop_groups(bool)

Registers this class to receive change updates on all nexthop groups.

Expects a boolean signifying whether notifications should be propagated to this instance or not.

void watch_nexthop_group(std::string const & nexthop_group_name, bool)

Registers this class to receive change updates on the given nexthop group.

Expects the name of the corresponding nexthop group and a boolean signifying whether notifications should be propagated to this instance or not.

virtual void on_nexthop_group_active(std::string const & nexthop_group_name, bool active)

Handler called when the active status of a nexthop_group changes.

class nexthop_group_iter_t

Private Functions

nexthop_group_iter_t(nexthop_group_iter_impl * const)

Friends

friend class nexthop_group_iter_impl

class nexthop_group_mgr

#include <nexthop_group.h>

A manager of ‘nexthop-group’ configurations.

Create one of these via an sdk object prior to starting the agent main loop. When your eos::agent_handler::on_initialized virtual function is called, the manager is valid for use.

Public Functions

virtual ~nexthop_group_mgr()

virtual void resync_init() = 0

virtual void resync_complete() = 0

virtual nexthop_group_iter_t nexthop_group_iter() const = 0

Iterates over all the nexthop groups currently configured.

virtual nexthop_group_t nexthop_group(std::string const & nexthop_group_name) const = 0

Retrieves an existing nexthop_group_t by name, if it exists. Otherwise this returns an empty `nexthop_group_t()`

virtual nexthop_group_entry_counter_t counter(std::string const & nexthop_group_name, uint16_t entry) const = 0

Returns the counter corresponding to the given nexthop group name and entry, if it exists. Otherwise this returns an empty ‘nexthop_group_entry_counter_t()’

Counters are reset whenever nexthop group entry configuration changes.

virtual bool exists(std::string const & nexthop_group_name) const = 0

Returns true if a nexthop group with the given name has been configured.

virtual bool active(std::string const & nexthop_group_name) const = 0

Returns whether or not the given nexthop group is active.

Nexthop groups are active if the FIB has prefixes using this group. Deleting an active nexthop group will cause all prefixes that point to that nexthop group to blackhole their traffic.

In order to hitlessly delete a nexthop group, first delete all prefixes that point to it, wait for the nexthop group to no longer be active (using nexthop_group_handler::on_nexthop_group_active), and then delete the nexthop group.

virtual void nexthop_group_set(nexthop_group_t const &) = 0

Creates or updates a nexthop group.

virtual void nexthop_group_del(std::string const & nexthop_group_name) = 0

Removes the named nexthop group from the configuration if it exists.

Protected Functions

nexthop_group_mgr()

Private Members

nexthop_group_mgr

Friends

friend class nexthop_group_handler

Type definitions in nexthop_group

Warning

doxygenfile: Found multiple matches for file “eos/types/nexthop_group.h