def solve(self, topo, requirement_dags):
# a list of tuples with info on the node to be attracted,
# the forwarding address, the cost to be set in the fake LSA,
# and the respective destinations
self.fake_ospf_lsas = []
self.reqs = requirement_dags
self.igp_graph = topo
self.igp_paths = ssu.all_shortest_paths(self.igp_graph)
# process input forwarding DAGs, one at the time
for dest, dag in requirement_dags.iteritems():
logger.debug('Solving DAG for dest %s', dest)
self.dest, self.dag = dest, dag
self.add_dest_to_graphs(dest, dag)
if dest not in topo:
sinks = dag.predecessors(dest)
for s in sinks:
logger.info('Adding edge (%s, %s) in the graph',
s, self.dest)
topo.add_edge(s, dest, weight=self.new_edge_weight)
for n in topo.nodes_iter():
if n == dest: # dest is a path in itself
self.igp_paths[n] = ([[n]], 0)
continue
paths = []
cost = sys.maxint
for s in sinks:
if s not in self.igp_paths[n][0]: # no path to sink
continue
c = self.igp_paths[n][1][s]
p = self.igp_paths[n][0][s]
if c < cost: # new spt
paths = list(ssu.extend_paths_list(p, dest))
cost = c
if c == cost: # ecmp
paths.extend(ssu.extend_paths_list(p, dest))
if paths:
_t = self.igp_paths[n]
_t[0][dest] = paths
_t[1][dest] = cost
self.complete_dag()
# Add temporarily the destination to the igp graph and/or req dags
if not self.solvable(dest, dag):
continue
for node in nx.topological_sort(dag, reverse=True)[1:]:
nhs, original_nhs = self.nhs_for(node, dag, dest)
if not self.require_fake_node(nhs, original_nhs):
logger.debug('%s does not require a fake node (%s - %s)',
node, nhs, original_nhs)
continue
for req_nh in nhs:
logger.debug('Placing a fake node for nh %s', req_nh)
self.fake_ospf_lsas.append(ssu.LSA(node=node,
nh=req_nh,
cost=-1,
dest=dest))
return self.fake_ospf_lsas
def solve(self, graph, requirements):
"""Compute the augmented topology for a given graph and a set of
requirements.
:type graph: DiGraph
:type requirements: { dest: DiGraph }
:param requirements: the set of requirement DAG on a per dest. basis
:return: list of fake LSAs"""
self.reqs = requirements
log.info('Preparing IGP graph')
self.g = prepare_graph(graph, requirements)
log.info('Computing SPT')
self._p = ssu.all_shortest_paths(self.g)
lsa = []
for dest, dag in requirements.iteritems():
self.ecmp.clear()
log.info('Evaluating requirement %s', dest)
self.dest = dest
self.dag = dag
log.info('Ensuring the consistency of the DAG')
self.check_dest()
self.complete_dag()
log.info('Computing original and required next-hop sets')
for n, node in self.nodes():
node.forced_nhs = set(self.dag.successors(n))
node.original_nhs = set([p[1] for p in
self.path(n, self.dest)])
if not self.check_consistency():
log.warning('Consistency check failed, skipping %s', dest)
continue
log.info('Placing initial fake nodes')
self.place_fake_nodes()
log.info('Initializing fake nodes')
self.initialize_fake_nodes()
log.info('Propagating initial lower bounds')
self.propagate_lb()
log.info('Reducing the augmented topology')
self.merge_fake_nodes()
log.info('Generating LSAs')
lsas = self.create_fake_lsa()
log.info('Solved the DAG for destination %s with LSA set: %s',
self.dest, lsas)
lsa.extend(lsas)
return lsa
